KDE Plasma 5 hangs on splash screen

Symptoms: KDE Plasma 5 splash screen starts after login (e.g. from sddm), spins for a while, then pointer cursor appears and can be moved, but no desktop ever appears. Other DEs (Enlightenment, GNOME, Windowmaker, FVWM, TWM, MATE, etc.) work without issues. New user or any user immediately after a reboot can get to desktop once; therefater, plasma hangs during splash screen. However, this does not affect root GUI logins to plasma. Affects base plasma, plasma(full wayland), and plasma(wayland). Problem appears after recent updates.

Cause: stale “plasma_session” processes persist after logout and interfere with new logins. Versions:
Name : plasma5-session
Version : 5.18.5-lp152.2.1

Name : plasma5-workspace
Version : 5.18.5-lp152.2.1

Name : plasma5-addons
Version : 5.18.5-lp152.1.2

Name : plasma5-defaults-openSUSE
Version : 84.87~git20190606T185118~3d37a0c-lp152.12.2

Name : plasma5-desktop
Version : 5.18.5-lp152.2.1

Name : plasma5-integration-plugin
Version : 5.18.5-lp152.1.2

Name : plasma5-session-wayland
Version : 5.18.5-lp152.2.1

Name : plasma5-theme-openSUSE
Version : 84.87~git20190606T185118~3d37a0c-lp152.12.2

Name : plasma5-workspace-libs
Version : 5.18.5-lp152.2.1

Workaround: Log in on a tty (e.g. tty2) as root and kill stale plasma_session processes.

Hardware specs are needed.

Please edit ‘/etc/systemd/logind.conf’ – the parameter you need is “KillOnlyUsers” – when a user logs out, kill all the remaining processes of that user – bad for the case that, a user wants specific processes to remain executing after that user logs out …
[HR][/HR]Quoting the man page:

       KillOnlyUsers=, KillExcludeUsers=
           These settings take space-separated lists of usernames that override the KillUserProcesses= setting. A user name may
           be added to KillExcludeUsers= to exclude the processes in the session scopes of that user from being killed even if
           KillUserProcesses=yes is set. If KillExcludeUsers= is not set, the "root" user is excluded by default.
           KillExcludeUsers= may be set to an empty value to override this default. If a user is not excluded, KillOnlyUsers= is
           checked next. If this setting is specified, only the session scopes of those users will be killed. Otherwise, users
           are subject to the KillUserProcesses=yes setting.