External USB-C Monitor randomly loses signal to MBP for 1-2 seconds

[sutterseba]

So this is an issue I had for quite a while, I searched for similar issues online and literally found nothing, only some old stuff from 2013, which doesn't help me at all. That's why I'm here. My MacBook is also out of warranty thence I don't get free technical support from Apple so I'm kind of on my own with this one.

I'm using a 2018 MBP 13" with these specs:
MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports)
2,3 GHz Quad-Core Intel Core i5
8 GB 2133 MHz LPDDR3
Intel Iris Plus Graphics 655 1536 MB

My current Monitor is this one, using it with the Thunderbolt cable that comes with it. I am also using the Monitor as a Hub for LAN-Input, AUX Input and the receiver for my BT mouse, I don't know whether that's relevant.

LG 27UL850-W 68,58 cm (27 Zoll) UHD 4K Monitor (IPS-Panel, USB Type-C, VESA DisplayHDR 400), schwarz weiß

Mit dem 27UL850 präsentiert LG einen neuen Ultra HD 4K Grafik Monitor mit VESA DisplayHDR 400 und HDR10 für PC. Sein AH-IPS Panel überzeugt mit großem 99% sRGB Farbraum, Ultra HD Auflösung, feinem Detailreichtum und Hardware Kalibrierung. Umrahmt vom nahezu rahmenlosen Displaydesign und neuem erg...

amzn.to

Now for the actual problem:

Sometimes, completely random, the Monitor loses connection to the MBP for a very brief moment, sound also changes from the Monitor output to the MBP Internal speakers, until it comes back and everything is just fine. I absolutely have no idea what this is about and how to solve this. Initially I thought it has something to do with the Monitor or the TB cable but I have checked it with my Razer Blade via USB-C, so basically the very same usage, just on a Windows machine, and I didn't have the issue. My next thought was that the TB port on the MBP maybe had some sort of loose contact, but, same issue for all four TB ports.
I also tried to separately charge the MBP with the original charger instead of only relying on the monitor (thinking that maybe the MBP gets kicked out of clampshell because power supply interrupts) but that didn't help either.
And again, it's not like every 60 seconds my screen goes black, it happens quite rarely and totally random. Every 5-6 hours seems a realistic estimate. Now I know, that is not a serious issue, but with a 500$ Monitor and 1400$ Laptop, that sort of issue shouldn't even come up in the first place.

Yes, I did a PRAM & SMC reset.

I just hope that someone can help me out with this and/or has experienced something similar.

Thank you guys

 

[PhabulousPhab]

Hi. I don't know if you will see this. But I still signed up as I have the same problem. Exactly the same LG model and also connected via USB-C. I use a new M1 MacBook Air. It worked fine on my MacBook Pro before. With the M1 I also experience occasional losses of the connection, which is really annoying. Did you ever find a solution?

I was desperate enough to even install LG OnScreen Control from LG's website and LG Screen Manager from the App Store to find a firmware update or something. Neither app works as both don't recognize the connected screen.

 

[rcgregory]

Hi Phab- Just set up a new M1 Macbook Pro yesterday with an external HP V27i monitor (connected via Thunderbolt 3 to Anker Hub to HDMI). This morning I noticed the same behavior you described. Prior Macbook Pro (most recent 2020 Intel version) never did this. My HP monitor is about a month old. I will continue to monitor to see if this persists and report back. Good luck.
-RC

 

[PhabulousPhab]

Hi RC! Thanks for sharing your experience. So there seem to be some issues with external (USB-C) monitors and M1 MacBooks. It can be annoying as sometimes the lost connection will not reestablish automatically, but you need to reconnect the cable. The connection is not fully lost, though. It's still utilizing the USB-A devices connected to ports on the monitor. There's just no more image on the screen / signal to the monitor and MacBook's system settings also don't show a connected screen anymore when it happens. And it happens completely random!

One more thing which may or may not be related:

I noticed something else and it took me ages to figure out the reason. If you have a bluetooth headset, try the following: Connect it to your Mac and start a video conference while also using the external monitor. Using Google Hangouts I can reproduce that this will make the M1 ridiculously slow, there even is a significant delay when typing. But as soon as I disconnect the monitor OR switch back to a non bluetooth audio device, all is well again. No issues like this on my previous Intel MacBook Pro. And also annoying as I do a lot of video calls during the pandemic and usually used my Beats X headset for this. Now I have to use a wired solution or disconnect my monitor, which is not really an option.

 

[rcgregory]

Since updating to OS 11.1, this display problem seems to have disappeared. Fingers crossed.

 

[PhabulousPhab]

In my case the problems rather have changed but not disappeared. Every now and then the MacBook will simply not output to the external monitor. And when I reconnect the cable, the MacBook sometimes crashes and reboots right away. Can't say I am too happy with these changes, haha.

 

[WBrimley]

Finally I found a thread with the exact problem I am having. I am using a MBP 2019 and an 38" LG Widescreen. This is a terrible problem because at night it causes the monitor to display (at total random intervals) the NO SIGNAL screen which brightens up the entire room and wakes me up. Has ANYONE found a solution to this or Apple been made aware?