After looking through other processes that use CPU while selecting text, I noticed clipit there as well. Closing clipit seems to improve things a lot. I still see gnome-shell go to 25% CPU but the UI is responsive now.
** This bug is no longer a duplicate of bug 1850969 x11 session all mouse or keyboard action ignored -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1850995 Title: gnome-shell: freeze and high CPU usage To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1850995/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs