Dual monitors not working on Ubuntu 22.04

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I have trying to run 2 4K monitors from an HP t630 thin client. It has 2 display ports.

With some trouble I got it working on the monitors at my desk but when plugging in to the wall mounted monitors I cannot get it to have both monitors on at once. Using the gnome display manager I can see both monitors. When I ask it to mirror both screens go black and it just reverts after the timeout. Trying to join the monitors I change the settings of the second monitor to match the first and click apply and I can see the display settings applet in the background revert back to single monitor even though I click to keep the settings. The refresh rate of the second monitor reverts to 60Hz when I am trying to set it to 30Hz but nothing appears on it.

I can plug either monitor in individually and it works and remembers the scaling and refresh rate but as soon as I plug one in as a second monitor it does not remember these settings.

It is driving me crazy as it worked successfully, although temperamentally with the monitors of the same model on my desk.

If relevant I am using Xorg (as I need to use devilspie2) but had the same issue with Wayland so I don't think the problem is WM related.

I looked in ~/.config/monitors.xml and updated any settings in here that weren't correct. Then I restarted. I also tried deleting this file and starting again like they were new monitors to see if this would help.

I also have another HP thin client, the t730 model, doing the same task on the same monitors without issue.

Any suggestions how I can solve this?

I sit in a Tesla and translated this thread with Ai:


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