i am not on 6 yet - but i find when 5.5.X is having trouble with stability in 64 bit a plug in is often culprit (with native instruments’ stuff i have had the 32 bit dlls drop in my 64 bit folder - so making sure all those ducks are in a row helps)
Also watch out for all the security dongles out there - i have also found that when my elicensor or ilok arent up to snuff - it can cause some crashing sillyness… seems obvious but i cant tell you how often I getting all heated at cubase… then quickly realize (palm to face)