Can not access desktop after switching user: stuck at "authentication required to refresh system repositories"

[leonardo]

When switching from the user (sudo-enabled) I normally use to another one (which I rarely use, and is also sudo-enabled), I can not access the desktop.
A window opens blocking the whole screen and asking the user password (the second user), whatever I type, the window does not close (see screenshot). In some cases after a random number of times I push "cancel" the window disappears, but not all the times.

Steps to reproduce the bug:
 - switch from user A to user B
 - enter password in gdm, log-in is successful
 - update window opens and never disappears. I can not access the desktop.

To exit this situation I need to change desktop with CTRL+ALT+F4 and log-in again with user A, which works. If I switch to user B again I am stuck again.

Note that after this happens, I updated/upgraded repositories using user A and the window will be still there when switching to user B.

What you expected to happen:
 - If I enter the user password the window should do something (start updating) but instead it produces an error (something on the line "This did not work") and the window remains there
 - If I push "cancel" the window remains there, only in some cases it did disappear after clicking cancel many times (tens of times)

I'v seen this page describing something similar, but I don't have xRDP installed

https://c-nergy.be/blog/?p=14051

$ dpkg -l| grep -i xrdp
$

Ubuntu Version: packages updated to March 13 2020.
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 19.10
Release: 19.10
Codename: eoan

GNOME: 3.34.2
Graphics: Intel UHD Graphics (Whiskey Lake 3x8 GT2)

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

To change the source package that this bug is filed about visit https://bugs.launchpad.net/ubuntu/+bug/1867319/+editstatus and add the package name in the text box next to the word Package.

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]

[leonardo (u-cail-c)]

I see that the user has tens of /usr/lib/policykit-1/polkit-agent-helper-1 processes running, which seems to be part of the policykit-1 package

[leonardo (u-cail-c)]

Edit on the previous comments, the processes are not owned by the user, processes are owned by root but ps returns several lines like:

/usr/lib/policykit-1/polkit-agent-helper-1 USERNAME

where USERNAME is the user that gets stuck