you're using the nvidia driver, and since it seems to be a bug in the driver, there's nothing much we can do about it
also, 340 series was just annouced to be EOL ** Package changed: xorg-server (Ubuntu) => nvidia-graphics-drivers-340 (Ubuntu) -- You received this bug notification because you are a member of compiz packagers, which is subscribed to compiz in Ubuntu. https://bugs.launchpad.net/bugs/1853707 Title: Whole system stopped responding because of single program's fault - no way out, had to force power off To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/compiz/+bug/1853707/+subscriptions _______________________________________________ Mailing list: https://launchpad.net/~compiz Post to : compiz@lists.launchpad.net Unsubscribe : https://launchpad.net/~compiz More help : https://help.launchpad.net/ListHelp