Update for anyone maybe with similar problems.
I noticed the crash was happening when the project was loading a certain vocal track. I knew this track only had the cubase pitch correct plugin on.
so…
I opened the project on cubase 6.5 on another PC i had. It opened fine. i deleted the pitch correct plugin on the track, saved project and opened back on 8.5.
All works now. So me thinking and blaming a third party plugin was wrong when its Cubase own plugin.