It just happened after booting with monitors disconnected and then connecting the monitor. Ubuntu offered to file a bug with more information https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1968712 collected on its own so I will try to close this one and we can follow there.
Edit: apologies, it seems I don't know how to close the bug here, none of options seems appropriate -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1968705 Title: one external monitor unresponsive after suspend To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1968705/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
