It happens a lot when the notification pops out. I need to restart the gdm.service to make it work.
The same issue here. I disabled notifications for the time being and I'm waiting for the next gnome-shell (or mutter) update.
It seems that fixed with gnome-shell 1:3.34.1+12+ga43c22e3a-1 and mutter 3.34.1+52+g403d8fcc6-1.