tell you: only thing I have not try in your list (BTW. thank!)

-  Have you tried deleting the preferences and uninstalling and reinstalling the program? If not, try doing that too.  The preferences are located in [User folder]> AppData> Roaming> Poser.  They are all contained within the 8.0 folder.  Just make a copy of that folder, and then delete the original.  (Use the copy to restore the settings in case resetting them doesnt work.)
I use to delete the TEMP in same location(almost same).

Never crashes when I rendering. It render or it render not. If I put too much heavy stuff in the render and go for the MAX of Max settings then won't do it! ODD!
Freezes when I delete anything from the scene like 80%.
Closing a doc. and opening other happens to crashes! About 50%
Won't like to import an object..that's odd. I'm obliged to import it from Poser Pro and save and then go with it as > import a pz3 then goes perfect.

Actually I'm going to live with that...untill a pacht shows up to fix it.
I'll not mess up with my new system, new OS and all newly installed  because of <poser
That's a decision I did today..its getting too far.

Thanks for your help, and post here when  you hear something has  definitevelly fix all the bugs in P8. - for us using Win 7 64 bits.
thanks
Cris

"'you shut up!  or I'll bring democracy to your country! "
Cris Galvão aka Softcris  - www.crisgalvao.com
(or softcris, SoftCris)
Rendering since 1997 and
at Renderosity since 1999.
OS Win 8.1     64 bit