Problems with running 2x monitors on HDMI


I received my TBT3-UDZ just on Friday here in the UK. Sadly, I am also having problems with running 2x monitors on HDMI.

My current computer is a MacBook Pro 16" from late 2019. My monitors are Dell U2718Q.

I have been using these monitors for over 2 years now with my old Thunderbolt 2 setup with my previous Mac and since getting the new one, I have been using a TB3 to TB2 adapter. I had two TB2 docks daisy-chained with each one driving a monitor.

What I have noticed is that it does seem to work intermittently, when the lid of the MacBook is open. However, I use it in clamshell mode and soon it will be sat in a vertical dock. What I am finding is that one of the monitors drops right down in resolution. The highest option is 2048x1080. Everything looks completely zoomed and blurry. The other monitor works fine.

If I boot into Windows using Bootcamp, both monitors work fine. No problems. Maybe suggests a bug in macOS perhaps? I am running macOS 11.1 Public Beta 2.

I have tried resetting the SMC and the NVRAM/PRAM on the Mac, but it hasn’t made a difference.

Wondering whether to purchase some DisplayPort cables and try those instead but these HDMI cables are good ones and have been fine for the past 2 years.

Any ideas?



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

Looking at the diagnostics you sent in separately from this forum post, I don’t see any immediate red flags from a software perspective as far as the dock itself is concerned. The data about clamshell mode is interesting, that isn’t something we’ve had reported yet.

However, we have had other reports of similar issues with the public beta with incorrect resolutions over HDMI. Trying DisplayPort may be beneficial if able, but I’m uncertain if that will resolve the issue at this time.

I recommend reporting this bug if you can, the more users reporting this the better chances of it being resolved in the subsequent release of the next beta. I haven’t heard of this issue on a stable build so far.

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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