Comment # 1 on bug 1206769 from Stefan Dirsch

I don't think you need this extra 

  sudo prime-select offload-set intel

This should be the default anyway (using "modeset" driver and not "intel" if
you specify "intel2" here; confusing I know)

Could you provide a X logfile when you run into this issue? Unfortunately it
depends on your desktop/displaymanager where you can find it. :-( Probably
either
/var/log/Xorg.0.log or ~/.local/share/xorg/Xorg.0.log. Probably you need a
reset of the configuration first.

 sudo prime-select unset