Happened to me again. Just in case is of help:
1- Computer was some time idle with the browser opened.
2- Updated some flatpaks through the terminal with "flatpak update".
3- Closed the terminal
4- Closed the browser, and then it happened.
File attached following instructions on #20
And followin
It just happened to me, using X.org with and AMD graphics card and no extra
extensions enabled.
Upgraded from Ubuntu 20.10 to 21.04.
** Attachment added: "system-info"
https://bugs.launchpad.net/ubuntu/+source/gnome-shell-extension-ubuntu-dock/+bug/1922353/+attachment/5495658/+files/system-in
