Would you mind sharing more information about this? There are indeed limitations to what you can do during DLL/bundle loading and unloading and you need to be careful about system calls at this point, but I don’t see what should be different for VST3 audio plug-ins compared to other plug-in formats (which do not have this init problem), so I am probably missing something here.
Are you doing something special in the SDK or in Cubase that is supposed to break this?