pop-up notifications get out of sync
Reproduction scenario using notify-send:
$ notify-send aaa && notify-send bbb && notify-send ccc
$ notify-send zzz
After enter on the first line, 'aaa' is displayed then after enter on the second line, 'bbb' is displayed instead of the expected 'zzz'. Note that it doesn't matter how much time passes between the execution of the two commands.
This behaviour renders notifications from chat applications (like slack) useless since the notifications and the messages are always out of sync.
Note that the issue is not reproducible if the notifications are acknowledged (i.e if the user clicks on the notification, for example)
Tested with Gnome version 3.36.8 on Ubuntu 20.04.2 and Gnome 40 on Arch