After enabling the nvidia drivers for my optimus based laptop (Intel iGPU + nvdia discreet GPU), kwin crashed regularly. The main symptom was that application windows would not respond to mouse clicks, even though the mouse cursor still responded.

The fix was to create some symlinks in /usr/lib that pointed to a specific OpenGL library as apparently the nvidia OpenGL library was getting called by default (this should not be the case since optirun should be loading the nvidia libraries at run time).

This seems to have corrected the issue for now.