Downstream clone of bugreport https://bugs.kde.org/show_bug.cgi?id=410106
STEPS TO REPRODUCE
1. Log into an user (let's call it A). Open an application, for example Firefox, just to keep something opened on the screen.
2. Then open a new session and login into another user, (let's call it B)
3. Terminate B session
If you will login again again into A you will see that the A session has been terminated. I runned this check also by keeping users logged into IRC Freenode to check the exact time of disconnection (session termination)
Session A must not be terminated if session B is terminated
KDE Plasma 5.16.3
KDE Frameworks 5.59.0
A senior Fedora KDE user told me that this happens also on SDDM, GDM instead works well.
Fedora GNOME instead works well also on SDDM