Primary external monitor intermittently loses video for about five seconds

Thunderbolt TBT3-UDZ
1

The primary external monitor I am using with my TBT3-UDZ intermittently loses video for about five seconds, and then the video is restored. This happens maybe three or four times everyday, at seemingly random times throughout the day. However, I have never seen this video loss happen to my secondary monitor, only the primary monitor.

These two monitors are HP Z27 4K monitors attached to the TBT3-UDZ dock’s ports via a Belkin KVM switch (F1DN202KVM-UN-3). I am using a Belkin dual-head Display Port cable (F1D9020b06t) to connect the TBT3-UDZ with the KVM switch, and I am using two of these iVANKY HDMI cables to connect the KVM switch to the monitors.

I am using the TBT3-UDZ with a 2019 16" MacBook Pro (with AMD Radeon Pro 5500M) connected via the Thunderbolt cable which came with the TBT3-UDZ. I keep this laptop’s lid closed, so my two external monitors are the only active displays. This computer is running macOS Monterey version 12.0.1. I also saw in the Mac System Information app’s Thunderbolt section that the TBT3-UDZ dock is running firmware version 58.1.

I am running the two monitors at 3840x2160 resolution at 60 Hz with the UI scaled. The Mac System Information app’s Graphics/Displays section reports that it “looks like 1920x1080 @ 60 Hz”. My primary monitor is not rotated, but my secondary monitor is rotated 270 degrees (vertical orientation).

I have not seen this monitor video loss issue with the other computer I have connected to the KVM switch via a separate (but same type of) Belkin dual-head Display Port cable (a desktop computer running Windows 10 with an eVGA FTW3 GeForce RTX 3090 graphics card) nor the previous laptop I used on the KVM port which the MacBook Pro is now connected to. That previous laptop was a Lenovo ThinkPad x280 running Windows 10, and although I used a different dock to connect it to the KVM switch (a ThinkPad Thunderbolt 3 Workstation Gen 2 dock), I used the same Belkin dual-head Display port cable which I am now using with the MacBook Pro. These facts lead me to think the issue may be isolated to the MacBook Pro or the TBT3-UDZ dock.

One more thing: I bought this TBT3-UDZ dock refurbished from Plugable on eBay on October 20, 2021.

Can you help me with this issue?

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Hello Kevin,

Thank you for contacting Plugable support! Sorry to hear about this issue. I’d be more than happy to assist you.

If you temporarily bypass your KVM, do these issues with your monitors directly attached to the TBT3-UDZ dock continue? We do not perform any testing or officially support the use of our docks through KVMs as historically we have seen problems can occur.

If you do not encounter issues with the monitors directly attached to the dock without the KVM in use then we’ll know there is likely a low-level incompatibility between the video chipsets in the dock happening with the KVM.

If you do encounter issues with the monitors directly attached to the dock, we may be hitting some other kind of issue and will want to gather more information to find out what’s going on. We have a troubleshooting tool that helps us find out what is going on in situations like this. Please plug the dock with your monitors directly attached to it into your computer, then go to this page and follow the instructions there:

http://plugable.com/support/plugdebug

When emailing us the diagnostics results please reference ticket 363268 in the subject line, do not post the results here.

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry
Senior Engineer | Product Owner
Plugable Technologies

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