Hi Neil
I have a very similar system as you, and have experienced the same issue that you have!
I noticed that if I increase my buffer settings above 128 or 256 samples… Kontakt 5 will start working again without having to restart Cubase!
I especially have this problem when using Studio Drummer within Kontakt!
I believe you are right that Kontakt is sensitive… and possibly a resource hog!
I know we have super-fast hardware, but if the software isn’t optimized… it won’t make any difference!
Al