Hello,
I get randomly this error message when starting up my computer and starting KDE from either KDM or SDDM:
Plasma is unable to start as it could not correctly use OpenGL 2.
Please check that your graphic drivers are set up correctly.
Sometimes it's ok, starting KDE without this error, but mostly the error is present preventing to start KDE.
I have proprietary nvidia driver from Suse Nvidia repository. With nouveau it was even worse - hanging X when starting KDE.
Driver seems to be ok by looking on glxgears and Xorg log.

I noticed this error, not sure is related:
Code:
192:~ # systemctl -l status systemd-tmpfiles-setup.service 
 systemd-tmpfiles-setup.service - Create Volatile Files and Directories 
  Loaded: loaded (/usr/lib/systemd/system/systemd-tmpfiles-setup.service; static; vendor preset: disabled) 
  Active: failed (Result: exit-code) since Tue 2017-08-01 13:10:13 CEST; 3min 26s ago 
    Docs: man:tmpfiles.d(5) 
          man:systemd-tmpfiles(8) 
 Process: 503 ExecStart=/usr/bin/systemd-tmpfiles --create --remove --boot --exclude-prefix=/dev (code=exited, status=1/FAILURE)
Main PID: 503 (code=exited, status=1/FAILURE) 

Aug 01 13:10:12 linux systemd[1]: Starting Create Volatile Files and Directories... 
Aug 01 13:10:13 linux systemd-tmpfiles[503]: symlink(/dev/nvidiactl, /run/udev/static_node-tags/uaccess/nvidiactl) failed: No such file or dir
ectory
Aug 01 13:10:13 linux systemd-tmpfiles[503]: symlink(/dev/nvidia0, /run/udev/static_node-tags/uaccess/nvidia0) failed: No such file or directo
ry
Aug 01 13:10:13 linux systemd[1]: systemd-tmpfiles-setup.service: Main process exited, code=exited, status=1/FAILURE
Aug 01 13:10:13 linux systemd[1]: Failed to start Create Volatile Files and Directories.
Aug 01 13:10:13 linux systemd[1]: systemd-tmpfiles-setup.service: Unit entered failed state.
Aug 01 13:10:13 linux systemd[1]: systemd-tmpfiles-setup.service: Failed with result 'exit-code'.
192:~ #

There are various post on Internet about this error, but not with clear resolution.
There is this bug in KDE, but is closed:
https://bugs.kde.org/show_bug.cgi?id=375730

Thank you for any help.