HI,
Regarding each issue
1. For CPU usage when in hypershade or attribute edit this is expected results, the plugin at this time is caching
its shader cash this will happen each time u move slide when working with settings such as SSS or backscattering.
2. For displacement its possible your running out of gpu memory here. is it possible you can attach scene and provide
each step the lead you to this issue? and about opening new scene after this happen this seems interesting i would like to try
to reproduce this this sounds like a bug.
3. for volumetric lights can you provide you system specs and OS?
it is known that volumes will not work on MAC os