Comment 86 for bug 1824874

I have a reproducible test case, but you need to set up for VNC (I have a fresh 20.04 install, running headless, and this bug is a total PITA - it's pretty much permanent. Note that it's worse than the screenshot from comment #3 because the password is also viewable, and anyone can come along, click the eye icon, and see my password). If you don't want to vnc, see below.

In my case, I've installed the tigervnc server (tigervnc-standalone-server). Two changes to /etc/vnc.conf and you're good to go (note that no custom xstartup is required):

# must do this to connect remotely
$localhost = "no";

# set to whatever your remote screen size is
$geometry = "3840x2160";

polkit has issues with remote access and pops up lots of 'Authentication Required' windows. Eventually one will go in the top left corner and stay there, with the described behaviour. I think, but I'm not sure, that one way to trigger this is by hitting RET after entering your password, rather than the Authenticate button. Note that you may have to wait 10 or 15 minutes for another popup if the initial popups don't trigger this bug.

I've added a local polkit policy to try to get rid of the popups, to try to make a remote session look like a local session, which would hopefully get rid of the popups, but this isn't yet working. The Alt F2/r fix described above doesn't work.

If you don't want to run remotely over vnc, you should be able to trigger this by changing the default polkit policy for an app you use. See /usr/share/polkit-1/actions. A good one would be org.freedesktop.color.policy, which is the one which traditionally causes VNC problems ("create a color profile", etc). Find the 'allow active' lines, and replace the 'yes' with something like auth_admin/auth_admin_keep/auth_self_keep/etc. You'll then get the auth popups when you log in, and various time afterwards.