https://gitlab.gnome.org/GNOME/shotwell/-/issues/26
This issue is reproducible for me on two different systems. It's extremely disruptive when it happens, because my system is unusable until I reboot. Is there any chance we can get a bugfix released? Also, isn't this indicative of an issue in Wayland or GDM? It seems like when a client (process) exits, anything it displayed should be gone.