Steinberg will probably tell you to update to the newes Cubase version.
Did you update Kontakt to the newest version?
If yes, I would talk to Native Instruments first.
Btw: This will not directly fix your bugs, but Cubase should still not crash, even if the plugins crash. Would be nice if you could leave a vote here if you think the same:
Solution to crashes by plugins - Sandboxing (Crash protection) - Cubase - Steinberg Forums