System is unusable (crashes) after screen is turned off and afk system must then be hard rebooted to recover.

I received a message today about Ubuntu impish (21.10) having been released and I upgraded from hirsute (21.04) .

A large number of packages were installed and a lesser number removed. The computer then was rebooted and seemed normal except for web pages on which I was unable to use for example BitWarden password manager web page icon. This did not respond. It needed the page to be shut down and restarted.

Later I turned off the monitor and was afk for some while. When I returned the system did not respond to any mouse clicks and needed a hard reboot to gain control. This has happened twice prior to this report.

Before the update the Power manager was set to turn off the screen after 6 minutes. I wondered if having this set and manually turning off the screen could be a problem. I changed the Power Manager setting to 'never' but the system freeze still occurred after manually turning off the screen and being afk.

This problem occurred immediately after the upgrade and nothing in the system had been manually changed.