multiple monitors – Amd Ryzen 4750U Displayport MST Dock causes crash Ubuntu 20.04

I have a lenovo thinkpad p14s G1 with a ryzen 4750U. I have windows 10, manjaro 20 and ubuntu 20.04 in a triple boot running, fresh install. I have this dock to convert the usb C to two displayports. It works perfectly fine on windows, but on manjaro and ubuntu it crashes. It works with one monitor connected. However, when the second one is added, it crashes (OS freezes). I suspect an issue with the amdgpu driver.
Here is what I tried so far:

  • update to latest 5.11 mainline kernel
  • update amdgpu drivers

It didn’t change the behaviour.

How can I debug what is going on and maybe fix it myself?