I’ve upgraded a Raspberry Pi 400 from Ubuntu 21.04 to 21.10, however as firefox was removed from the dock, whenever I go to launchpad then drag the firefox icon back to the dock, as soon as the drag action commences the system becomes unresponsive. REISUB/REISUP sometimes works after significant delays. I’ve seen reports also of the same issue on Raspberry Pi 4 models. Reports also say they can ssh into the machine fine.
https://askubuntu.com/q/1369681/22776
https://raspberrypi.stackexchange.com/q/132683/134746
https://forums.raspberrypi.com/viewtopic.php?t=321682
Cause may be