In Fedora Rawhide / 33 - this works OK on 32 - user switching is not working in openQA testing:
the test is an automated version of https://fedoraproject.org/wiki/QA:Testcase_desktop_login so it does a lot of stuff, but it's failing when it tests user switching. At https://openqa.fedoraproject.org/tests/588557#step/desktop_login/70 it is logged in as user 'jim', and about to click 'Switch User...'. Clicking Switch User takes it to GDM - https://openqa.fedoraproject.org/tests/588557#step/desktop_login/71 - where it clicks on 'Jack Sparrow' ('jack') and enters the correct password. At this point it seems like the system briefly tries to start a session for jack but then something goes wrong, and it returns to GDM - https://openqa.fedoraproject.org/tests/588557#step/desktop_login/74 .
You can see a video of the test at https://openqa.fedoraproject.org/tests/588557/video ; the user switch attempt starts around 1:08 in the video, 20:00:20 in the timestamps. I'll attach logs here.
As desktop team just agreed that we should block the release on user switching going forward, I'm proposing this as a Fedora 33 Final blocker.
Created attachment 1682623 [details]
tarball of /var/log from the failed test
You can use journalctl --file var/log/journal/c8db120e5f2f4027bedf0238954b4297/system.journal --utc to see the journal. The failed attempt to log in as jack happens around 20:01:20 UTC (the test runner hit 'enter' on the password at 20:01:19). You can use similar commands to see the individual user journals, I think jack is 1001.
In my home instance of OpenQA, I switched on the KDE user switching again, and the test fails similarly for KDE sessions. I am including the logs from the tested machine.
Created attachment 1692179 [details]
Similar tarball with logs.
after switch asks for "Authentication Required. Authentication is required to access the PC/SC daemon"
The video is already purged, so I can't confirm exactly, but I see the same problem in F32 on my home laptop. Whenever one of the users is logged in, a second user login seems to briefly work (the desktop is shown for a second), but then it immediately returns to gdm.
Hopefully fixed in gdm 3.36.3 by https://gitlab.gnome.org/GNOME/gdm/-/merge_requests/100
Discussed during the 2020-07-20 blocker review meeting: 
The decision to classify this bug as an "AcceptedBlocker" was made as it violates the following criterion:
"User switching must work using the mechanisms offered (if any) by all release-blocking desktops in their default configuration."
We'll also need a 3.37 release for Rawhide. halfline is working on it now.