Created attachment 142076 [details]
Screen image capture of the output of "journalctl -e --user" command at the time of X server freeze while logging in to KDE5

I use the following commands on Manjaro Linux to switch to runlevel 3, also known as multi-user.target in systemd language:
sudo systemctl set-default multi-user.target
sudo systemctl isolate multi-user.target
This causes no problem. To switch back to runlevel 5 (graphical.target) the following commands are used:
sudo systemctl set-default graphical.target
sudo systemctl isolate graphical.target
This effectively launces SDDM on tty1 as expected. However, loging in to KDE5 is not possible. Graphical display on tty1 freezes before KDE5 is launched. It is essentially a black screen with a responsive but useless mouse cursor. tty2-6 are still usable as CLI. From tty2 I can get the following error message (see attached screen image) by issuing the command "journalctl -e --user".
Suspecting nvidia module/driver to be the culprit, I switched to nouveau driver, but the problem persisted, although I was able to launch i3 with this change (KDE5 would still not launch and would produce similar errors as attached).
This is 100% reproducible so far.