It’s a long known and documented, that a wide variety of different Cubase trouble symptoms can be triggered by a corrupted UserPreferences file.
So when some tome ago, I started experiencing very long load times even for relatively small projects, I investigated that as a potential problem source.
And then I documented my experience and the results of in depth troubleshooting on another thread (see below for link) in lots of detail.
Your case my have a different root cause than mine, because there are other reasons why the UserPreferences file may end up with corruption. But it is well worth it to follow the widely documented process to start Cubase with a new/clean UserPreferences file, to see if that maybe helps. Here’s just one older forum thread, but there are probably more:
p.s. This is the link to the thread about my specific experience with slow startup times due to a corrupted UserPreferences file.