Ubuntu 20.04 + T2000 + dual monitor + docking station + driver 455 => screen freeze

Dear community/support

My screens experience a freeze after login under Ubuntu 20.04 with the setup in the title. The laptop is a Lenovo P1 gen3 with a ThinkPad Workstation Dock Gen 2 (updated to latest firmware). Interestingly, the driver version 450 seems to have less issues (screen flicker a few times, but do not freeze). Any ideas why version 455 is having issues?
nvidia-bug-report.log (1.7 MB)

Thank you very much for any hint!

PS: Ubuntu 20.04.1 & 5.4.0-54-generic
PPS: No issues at all under Windows