I don’t find this is the case.
Orchestra instruments with 10 Kontakt instances 16outs each. PSP plugs, RobPapen synths, Sylent1, IK Stuff, Nebula trough bridge emulation, Ozone, Melodyne, and some external hardware. All works like a charm under Logic, not same in Cubase.
I would suspect the fault lies within one or more of your many third party instruments/plug-ins not playing nice with Cubase. I’d figure out which one(s) are the problem through methodical trial-and-error and then contact the developer so they can sort out the compatibility issue their software is having with Cubase.