15-Inch MacBook Pro Display Stutter with External Monitor

Hello,

I just got a branch new 2018 15-Inch MacBook Pro (with Radeon Vega 20 graphics) and a Thunderbolt 3 Display (the NEC EA271U). The NEC monitor does not come with a Thunderbolt 3 cable so I got a 1.5ft Nektech Thunderbolt 3 cable from Amazon that is rated for 40Gbps data transfer and 100W PD.

I can observe a visible momentary freeze of the picture that occurs roughly every 3 seconds.

The freeze happens on both the MacBook internal display and on the external NEC display when the NEC display is connected. It happens regardless of the scaled resolution selected for the NEC display (I always left the internal display running at its default resolution).

This happens also when the laptop lid is closed and the external NED monitor is the sole display for the MacBook.

The NEC provides 60W of power over the USB-C cable to the MacBook so the MacBook is always charging and always using the Vega 20 graphics. The 60W is less than the peak power usage requirements of the MacBook Pro (covered by the 87W adapter). The issue still happens when I plug in the MacBook to the 87W power adapter (and verify in the System Report that the MacBook is drawing 87W of power from the power adapter as opposed to 60W from the NEC display).

The issue happens when Graphics Switching is turned off in Energy Saver. All 4 ports exhibit the problem.

I happen to own another 2017 MacBook Pro, which also exhibits the same problem, and a 2018 MacBook Air, which does not have this problem. Based on all this, it does not appear like an issue with the cable or the monitor or the specific laptop.

I am running the latest macOS Mojave 10.14.3 on all three laptops.

I have tried tweaking Energy Saver and other settings on the monitor, to no effect.

Oddly enough, when I return to my laptop and resume it from the beginning sometimes the issue disappears. After switching things around the issue comes back and once there, I am not able to find out a way to get it to go away. I have not been able to figure out under what conditions the issue goes away.

Has anyone else experienced anything similar?

Here are videos demonstrating the issue:

- You can clearly see the picture freeze at .41 seconds.

- You can see the picture freeze exactly every 3.15 seconds three times in this 9-second clip: at
* 1m 09s 13
* 1m 12s 28
* 1m 15s 43

And for those who might question this being a software issue / glitch, here is a video showing how mouse cursor motion freezes as well, and GPU + CPU utilization on the machine, showing there is no system overload of some sort:


Thank you for reading.

--- Post Merged, Mar 14, 2019 at 5:41 AM ---

So it appears the issue only occurs when unplugging the monitor and plugging it back in while the laptop is running.

When cold (re)booting the laptop from power-off or resuming from sleep with the monitor cable already plugged in (and most of the time when plugging the cable in for the first time after a cold boot/resume) the monitor works fine - there are no 3.15 second periodic freezes / stutters.

Disconnecting the monitor and reconnecting it again while the laptop is running causes the 3.15 stutters to begin. Every. Single. Time. (The stutters only happen while the external monitor is connected).

Note: I do not possess any Thunderbolt 3 to DisplayPort or HDMI adapters to test other connectivity options. I do not have other external monitors in my possession to test either. I am planning on visiting an Apple Store and asking for help to test for this problem using the Apple Store-offered LG monitors) using my laptop and my thunderbolt 3 cable.

 

Update 2: Had a chat with Apple Support, they had me reset the SMC controller, which did not help, and I am set for an appointment in the store tomorrow.

--- Post Merged, Mar 14, 2019 at 6:45 AM ---

Thanks for sharing your experience and the clarification about the display not being a "thunderbolt 3 display." I am trying to make sense of it all and it seems all displays are DP-over-USB-C connector using a Thunderbolt 3 cable usually (as it needs to be rated 20Gbps at least if you want 4K UHD 3840x2160 video at 60fps with 30-bit color adds up to >15Gbps which is above the USB 3.1 10Gbps speed).

Other than older monitors that I have heard about that used to be able to daisy chain using prior versions of Thunderbolt, are there any current monitors that actually use any Thunderbolt 3 functionality (for daisy-chaining or for picture data transfer) vs just doing DP over a USB-C connector cable that is likely rated to support Thunderbolt 3 speeds?

 

Thank you for the input jaytv111.

I am still interested in hearing some backing to the Thunderbolt 3 vs USB-C monitor claim.

What makes a monitor qualify as a "Thunderbolt 3" monitor? Given that based on everything I read out there, the only way people send video over USB-C cables today is via the DisplayPort protocol, which natively runs alongside both the USB 3/3.1 protocol and the expanded-capabilities Thunderbolt 3 protocol. Or is there a native Thunderbolt 3 protocol for driving a display? Or is it simply that the monitor has something akin to a built-in Thunderbolt-3 dock that passes through DisplayPort data to the Display and has USB ports that can run at high speed? (My NEC caps USB port speeds to USB 2.0 speeds and if I want USB 3 speeds I have to give up 4K UHD at 60Hz and downgrade to 30Hz which is naturally unacceptable).

--- Post Merged, Mar 14, 2019 at 11:24 AM ---

It sure could, although it would be strange that the MacBook Air is able to drive the monitor no problem at the same resolution and same refresh rate with that same cable (using its much weaker Intel integrated graphics), while two MacBook Pros with two generations of different discrete AMD graphics fail to do so properly (under certain conditions).

--- Post Merged, Mar 14, 2019 at 11:48 AM ---

So I guess the best way I can answer my "Thunderbolt 3" monitor question is with the following quote from the LG UltraFine 5K product description: "Plus, three USB-C downstream ports (USB 5 Gbps) let you connect additional devices as needed."

As I already mentioned, the ports on my NEC EA271U are limited to USB 2 speeds (480 Mbps) unless I downgrade from to 30Hz (at the max 3840x2160 resolution), and I guess the reason for that is that the monitor is only capable of using USB 3/2 + DisplayPort over the USB-C cable and that cannot carry as much data as Thunderbolt 3 + DisplayPort can.

These protocols are so vaguely documented online that it makes my engineer heart cringe. If I can run DP alongside USB 3 over my USB-C link, then who determines the maximum speed? Does the DP data count towards the USB 2/3/3.1 data rates of 480Mbps/5Gbps/10Gbps? How does that make sense since the protocols are independent and running alongside each other as mentioned in some articles online?

Okay, now this is making some sense:

"Thunderbolt 3 is bi-directional with four lanes of PCI Express Gen 3 and eight lanes of DisplayPort 1.2."
- https://thunderbolttechnology.net/blog/difference-between-usb-c-and-thunderbolt-3

What does USB 3.1 support?

"4K @60Hz 24-bit color (without compression) with simultaneous USB 3.1"
- https://www.displayport.org/displayport-over-usb-c/

Okay, so if my display is 4K 30 but using 30-bit color maybe that is why it caps USB to 2.0 speeds (that option is not listed in the article above, but the next option kind of caps things as 4K with 30-bit color might fall somewhere between 4K and 5K with 24-bit color:

"5K (5120 x 2880) display support without compression with simultaneous USB 2.0"

Hope this is might be helpful to others looking for the same info.

 

Just tried Apple's 0.8m Thunderbolt 3 cable. Problem still exists. Displays still stutter continuously every 3.15 seconds after reconnecting the external monitor while the laptop is running.

 

I was at the Apple Store today. Connected to an external 21.5" LG UltraFine 4K display using both USB-C Thunderbolt cables in my possession - the Apple one and the cheaper one from Amazon. Both times the LG worked flawlessly, no stutter whatsoever after disconnecting and re-connecting the cable several times.

At home, the NEC monitor still exhibits the issue every time I disconnect and reconnect it without putting the MacBook to sleep. I have decided I really like the NEC monitor and will work around the problem for the time being - putting the computer to sleep for 30 seconds resolves the issue every time.

My support rep at the Apple Store was really nice and took the time to take detailed notes on my case and escalate to Apple Engineering.

I am going to be in touch with NEC support as well over the next few days. Will keep this thread updated for the benefit of anyone else out there who might be running into the same issue.