Authentication Required window stuck after login

I am using Ubuntu 20.04 and need help with this:

The Authentication Required window is stuck and I can't close it :(

Would the Authentication Required window disappear if I reboot?

Are there other ways to solve this?

I faced the same problem on Pop_!OS, no need to reboot actually;
The easier way is to just restart GNOME by one of two ways:

• pressing Alt + F2, type r then Enter, or
• in terminal, killall -3 gnome-shell

This should just restart Gnome Shell. You will not lose your open windows, but you should be reminded to save all your work regularly!

Related bug: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1824874

Thank you for the nice tip!

For me it started happening seemingly all of a sudden. I am on a fresh Linux installation. Other than playing around with power management (suspend and hibernate) to make them work better, I did not fiddle around with anything else. It is happening after I login from suspension/reboot.

After a couple of days of trying to understand what might be wrong, I noticed a couple of things:

• When trying to restart the window did not only display the 3 buttons Cancel, Restart, Power off BUT it stated that there is another user logged in (with the same name as me). I checked how many users were logged in but there was only one (me)
• The authenticate window popup was popping up when I was trying to reboot (with the message ~= "authentication is needed for reboot")
• All of a sudden the brightness control stopped working and my screen brightness was not changing when I was updating the slider (I know weird...but again I had done nothing to fiddle around with it)

Those clues led me to think that the latest package I had installed might be the culprit. It was the "chrome remote desktop" package which is related to logging the user to the current active window session and touching on display properties..

And after uninstalling the package everything worked as before! No stuck authentication popups, no duplicate ghost users and I can control my display's brightness.

I hope those observations and my experience is useful to someone out there.