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I didn't see this thread, so I started a new one on this site for this particular issue. I'll delete that new thread..if possible. Anyway, I thought I'd add my experience with this issue and the 2018 Mac mini below.

I'm having the static/snow screen display issue after awakening from sleep on my 2018 Mac mini. By static/snow, I mean the monitor display looks like the pattern an old TV using an antenna would display if it lost its signal. I returned my first 2018 mac mini because of this issue and the replacement 2018 Mac mini has the same issue. What I've learned about this issue is documented below. Apple tech support seems very unaware and skeptical of this issue, so, in the near term, it's up to the community of users to figure this out. Please add any knowledge or experience you have with this issue to this discussion.

My 2018 Mac mini set up:
OS version as of this post: Mojave 10.14.2. The mini is connected to two Samsung C24F390FHN monitors. One monitor is connected via an HDMI cable to the HDMI port on the mini and the HDMI port on the monitor. The other monitor is connected to a USB-C port on the mini and the HDMI port on the monitor.
Issue Observations:
  1. The static/snow display issue ONLY occurs when the mini awakes from sleep mode. The issue started on the second day of usage after I received the mini. The issue did not on occur on the first day of mini operation. This was the case for both 2018 minis I have had.
  2. The issue ONLY occurs on the monitor connected to the HDMI port on the mini.
  3. The monitor connected via the USB-C port on the mini does NOT exhibit the snow/static display issue upon awakening from sleep mode.
  4. I isolated the issue to the HDMI port by switching how the two monitors were connected to the mini; either via HDMI or USB-C. Since the issue followed the HDMI port and not a specific monitor, this means either monitor is NOT the source of the issue. This issue is directly tied to the HDMI port on the mini.
  5. This issue is intermittent. After starting up the mini, the issue NEVER occurs the first time the mini awakens from sleep mode after startup. The issue randomly occurs during any subsequent wake up from sleep event. It can take several hours of the mini being on before the issue reveals itself.
  6. The issue seems to fix itself after less than a minute. The screen switches multiple times between displaying snow/static and a black screen and then eventually fixes itself.
  7. Disconnecting the HDMI cable from the mini or monitor and then reconnecting the HDMI cable also fixes the snow/static issue.
  8. Apple's tech support recommends three standard resets (PRAM, SMC and another acronym I don't recall), which do nothing for this issue. Don't waste your time performing these resets.
  9. Apple's tech support escalation process is ineffective for this issue. The third contact on my support case for this issue resulted in a Genius appointment that was a waste of time. The Genius stated that unless they can replicate the issue, the issue is likely specific to my computing environment. Rather than leave the mini at the genius bar for a few days, I chose to return the mini (it was only a few days old) thinking the issue was likely an anomaly only associated to the particular unit I had. That's not the case since my replacement mini has the exact same issue. My Apple tech support experience gave me the impression that since the 2018 Mac Mini is so new, Apple just doesn't have enough experience with this issue yet. Apple is very far away from becoming aware of its existence. Don't waste your time with a Genius appointment. You may even want to consider holding off on buying a 2018 Mac mini until this issue is figured out.
  10. Given that the HDMI port connected monitor works fine except for waking up from sleep mode, it sure seems like there's an OS bug somewhere in the HDMI port wake up instructions. Can and will Apple address said OS bug?
My next steps to get around this issue include:
  1. Try connecting both monitors via a USB-C port. As in, don't even use the HDMI port on the mini. This requires buying a new cable.
  2. If step 1 above doesn't work, then try using the HDMI port or a USB-C port on the mini to connect to the monitor via the VGA port or whatever other connection is available on the monitor besides the HDMI port. This requires buying a new HDMI to VGA cable or similar cable.
 
Re post 26 above...
Just wondering...

When you get "the snow" on the HDMI display, what happens if you:
a. Switch OFF the display for a few moments, then
b. Switch it back on?

Does that clear the snowfall?
 
I‘m using only one monitor ... an EIZO EV3285 connected via USB-C and I‘m expiriencing a similar issue: the Mac mini is sometimes not awakening from sleep. To be more precisely it is not the Mac which cannot awake himself, it‘s only the monitor which stays black after turning it into sleep mode to safe energy. For example I can still hear radio playing with iTunes in the background. When I move the mouse or press a key the monitor briefly goes ON and after few seconds it goes OFF because of missing signal on USB-C port.
Switching the monitor off and on, disconnecting and reconnecting the cabel doesn’t help to get the monitor running. The only one way is to reboot MacOS.
After upgrating MacOS from 10.14.1. to 10.14.2 the issue happens only very rarly but it is still there.
 
The options "Enable power nap" and "Wake for network access" may make the MAC system wake up during sleep .
So my USB-C to displayport cable arrived today. And indeed the results are much better. The original problem doesn't seem to be there, though there is a different problem now. Computer doesn't go to sleep every time.

Here is the summary -
1. On HDMI - Upon waking from sleep, computer wakes up with blank screen. Usually takes minutes for image to come up (if it does). Disconnecting and connecting the HDMI cable usually fixes it (it may take a couple of tries). Sometimes USB mouse doesn't work on waking from sleep. Disconnecting and reconnecting fixes it.
2. On Displayport (via thunderbolt port) - Computer wakes up as expected, and monitor instantly shows image. However, computer doesn't go to sleep every time. Sometimes monitor just comes back up. It may take a couple of tries to put computer to sleep. No USB mouse freezing thus far, but that's inconclusive.
Screen Shot 2018-12-31 at 9.32.25 PM.png
Screen Shot 2018-12-31 at 9.32.25 PM.png
Screen Shot 2018-12-31 at 9.32.25 PM.png
 
Hi - I just received my 2018 i5 mac mini a few days ago. I've been having problems with it displaying anything after waking from sleep. Every time I wake up the computer from sleep, the monitor is blank. The monitor backlight comes on when I wake the computer, but it's just a backlit black screen. I keep on trying various keys on the keyboard, or mouse and eventually it displays the screen. That too, not always. Sometimes even despite trying for 5-10 minutes the screen stays blank. I just have to force restart the computer.

I am using Acer monitor XB271HU, and have it connected via HDMI. I does seem like it's trying to perform the HDMI handshake but fails. Cause every time I press a key on the keyboard or mouse, the screen flickers or the backlight goes off and on for a quick moment. But most of the time the screen stays blank. I've had this monitor for over a year now, and never had this problem with my previous computer. So I am pretty sure it's not the monitor. The monitor does have a 'Deep Sleep' setting, which I have set to OFF.

Things I've tried so far -
1. Tried with a different HDMI cable.
2. Reset the computer's NVRAM by pressing Alt-CMD-P-R on start-up
3. Reset the SMC by simply shutting it off and taking out the power cable.

None of these things seem to work. Is anyone else experiencing this issue? Any solutions? Thanks.

I'm returning my 2018 mini today, for various reasons INCLUDING what you're experiencing here. I have the Asus XB271HU (IPS model) and have the exact situation. Screen goes blank (backlight on), intermittently comes back etc.

I just gave up on the 2018 mini for a myriad of issues, including this one.
 
I have this issue with my 2018 Mac mini (i5/16/512) and my LG 24UD58-B 4K monitor. There's a 50/50 chance that it would wake from sleep if connected via a USB-C/DP cable. It wakes up reliably if connected via HDMI. Something is definitely not quite right with the mini's DP video output.
 
I didn't see this thread, so I started a new one on this site for this particular issue. I'll delete that new thread..if possible. Anyway, I thought I'd add my experience with this issue and the 2018 Mac mini below.

I'm having the static/snow screen display issue after awakening from sleep on my 2018 Mac mini. By static/snow, I mean the monitor display looks like the pattern an old TV using an antenna would display if it lost its signal. I returned my first 2018 mac mini because of this issue and the replacement 2018 Mac mini has the same issue. What I've learned about this issue is documented below. Apple tech support seems very unaware and skeptical of this issue, so, in the near term, it's up to the community of users to figure this out. Please add any knowledge or experience you have with this issue to this discussion.

My 2018 Mac mini set up:
OS version as of this post: Mojave 10.14.2. The mini is connected to two Samsung C24F390FHN monitors. One monitor is connected via an HDMI cable to the HDMI port on the mini and the HDMI port on the monitor. The other monitor is connected to a USB-C port on the mini and the HDMI port on the monitor.
Issue Observations:
  1. The static/snow display issue ONLY occurs when the mini awakes from sleep mode. The issue started on the second day of usage after I received the mini. The issue did not on occur on the first day of mini operation. This was the case for both 2018 minis I have had.
  2. The issue ONLY occurs on the monitor connected to the HDMI port on the mini.
  3. The monitor connected via the USB-C port on the mini does NOT exhibit the snow/static display issue upon awakening from sleep mode.
  4. I isolated the issue to the HDMI port by switching how the two monitors were connected to the mini; either via HDMI or USB-C. Since the issue followed the HDMI port and not a specific monitor, this means either monitor is NOT the source of the issue. This issue is directly tied to the HDMI port on the mini.
  5. This issue is intermittent. After starting up the mini, the issue NEVER occurs the first time the mini awakens from sleep mode after startup. The issue randomly occurs during any subsequent wake up from sleep event. It can take several hours of the mini being on before the issue reveals itself.
  6. The issue seems to fix itself after less than a minute. The screen switches multiple times between displaying snow/static and a black screen and then eventually fixes itself.
  7. Disconnecting the HDMI cable from the mini or monitor and then reconnecting the HDMI cable also fixes the snow/static issue.
  8. Apple's tech support recommends three standard resets (PRAM, SMC and another acronym I don't recall), which do nothing for this issue. Don't waste your time performing these resets.
  9. Apple's tech support escalation process is ineffective for this issue. The third contact on my support case for this issue resulted in a Genius appointment that was a waste of time. The Genius stated that unless they can replicate the issue, the issue is likely specific to my computing environment. Rather than leave the mini at the genius bar for a few days, I chose to return the mini (it was only a few days old) thinking the issue was likely an anomaly only associated to the particular unit I had. That's not the case since my replacement mini has the exact same issue. My Apple tech support experience gave me the impression that since the 2018 Mac Mini is so new, Apple just doesn't have enough experience with this issue yet. Apple is very far away from becoming aware of its existence. Don't waste your time with a Genius appointment. You may even want to consider holding off on buying a 2018 Mac mini until this issue is figured out.
  10. Given that the HDMI port connected monitor works fine except for waking up from sleep mode, it sure seems like there's an OS bug somewhere in the HDMI port wake up instructions. Can and will Apple address said OS bug?
My next steps to get around this issue include:
  1. Try connecting both monitors via a USB-C port. As in, don't even use the HDMI port on the mini. This requires buying a new cable.
  2. If step 1 above doesn't work, then try using the HDMI port or a USB-C port on the mini to connect to the monitor via the VGA port or whatever other connection is available on the monitor besides the HDMI port. This requires buying a new HDMI to VGA cable or similar cable.
[doublepost=1550881795][/doublepost]You are correct stating "Don't waste your time with a Genius appointment" I did - it was a waste of time. I had the same problem with the snowy picture after wake up on my 2018 Mac Mini. My monitor was connected via the HDMI port - I purchased the USB- C cable and the problem was gone.
 
I've experienced the monitor wake-up delay with both a Mediabridge HDMI cable and a Cable Matters USB-C-to-DP cable. It was occasionally worse with the USB-C-to-DP cable as my LG 27UK650-W was clearly on but remained completely blank like the OP reported, but there's still a relatively significant delay with the HDMI cable, too.

It appears to me that my monitor is being woken up twice by the Mac Mini -- the first wake-up happens as quickly as I'm used to but with a blank screen, then it goes right back into power-saving mode even though the Mac Mini is already fully spun up from sleep, then the monitor wakes up again several seconds later with the normal login screen. Maybe this has something to do with the T2 chip?

Were you able to fix this problem?
 
I've upgraded the RAM from 8GB to 32GB few weeks ago. Since then NO black screens on wake up anymore!
No idea what caused the problem: faulty RAM ? ... faulty code which doesn't like to be swapped out ? ... or simply the disassembling and reassembling of the hardware ? ... However, I cross my fingers. It works now.
 
I've upgraded the RAM from 8GB to 32GB few weeks ago. Since then NO black screens on wake up anymore!
No idea what caused the problem: faulty RAM ? ... faulty code which doesn't like to be swapped out ? ... or simply the disassembling and reassembling of the hardware ? ... However, I cross my fingers. It works now.

With usb-c > DP i don't have the issues either.
 
I hope this helps you resolve the problem. It did for me.

TL;DR
2018 model Mac mini (purchased new in 2019 from Apple) will not wake HDMI connected monitor. Fails to do so every few days. Force power off of mac is only way to restart its HDMI port.

Solution:
Give up using the mac mini HDMI port... it has a design fault I believe.
Instead, connect the monitor using a Thunderbolt USB C to HDMI converter.
USB C at the mac mini, HDMI at the monitor.
Has worked for over a month without problem recurring.


DETAILS
I use my mac mini as my digital music source. Its on most of the time. When I am not using it I just use the shortcut key combination to switch off the monitor.

I use a Bluetooth Keyboard Mouse. The monitor is connected by HDMI.

When I go to use the Mac mini, tapping the keyboard or moving the mouse has zero effect - it will not wake the monitor ie: no signal sent to the monitor. The monitor screen stays off.

To try to resolve the problem I have:
Contacted Apple Support many many times
Allowed Apple remote access to "diagnose"
Reset SMC
Reset NVRAM (PRAM)
Used 3 different monitors (all HDMI connected)
Reset the mac to factory settings and then rebuilt it from scratch
Replace K/M with new Apple keyboard and mouse
Updated the OS many times over the last two years
Nothing fixed it.
Very, very frustrating.


Then I connected the mac mini to my monitor using USB C to HDMI converter. I used a ALOGIC Ultra USB-C (Male) to HDMI 4K (Female) Adapter from JB HiFi. This seems to have resolved it....over 6 weeks now and no repeat of the problem for me.
 
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