Public bug reported:

I have two external displays chained via Display port connected to the
ThinkPad Thunderbolt 3 Dock.

They are working with kernel 5.8.0-63 but not with the new 5.11.0-25
kernel.

I could reproduce this behavior several times for both kernels, as
follows: I booted up with disconnected dock, logged in, then I connected
it, disconnected it, and connected it again.

With the 5.11.0-25 kernel the external displays go black; the main
screen turns off and on several times. Sometimes the main screen remains
working, but UI is lagging.

I'm attaching the logs. Two separate boots for each variant are marked
'a'/'b'.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

** Attachment added: "logs_2021-08-05.zip"
   
https://bugs.launchpad.net/bugs/1938999/+attachment/5515989/+files/logs_2021-08-05.zip

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https://bugs.launchpad.net/bugs/1938999

Title:
  External displays not working on Thinkpad T490 with ThinkPad
  Thunderbolt 3 Dock

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