I’m running Cubase 8 Pro (latest) on Win 8.1. I have zero problems. No special OS tweaking and I run with the network (ethernet) connected - I use that iTunes networking so I can use Cubase IC Pro on an ipad to control the DAW. I use the UR-44 audio device. I stick with the H/W & S/W (plugins) that Steinberg sells. It keeps everything 100% stable.
I run Cubase IC Pro from my iphone 6+ and ipad 4th gen using IOS 8.3 - zero problems.
Thanks for the additional comment. Yeah, I use mostly VSL with a little CInematic Strings in Kontakt, all in VE Pro. I assume if an instrument is already working in my existing Cubase environment, and Cubase iC Pro is working for you in Cubase, then things should work with all my instruments. LOL. Perhaps that’s optimistic!