Ubuntu 21.10 bug on raspberry pi
I encountered this too [on 20.10].
It appears to be a known bug, and the updated test kernel provided as a work-around solves the problem for me.
More information here: https://bugs.launchpad.net/ubuntu/+source/linux-raspi/+bug/1946368
The link to the text kernel is contained in that thread... and their target is to get it in the mainline Ubuntu kernel by November 8th.