I’m sure it is on the list already: please develop a way to bypass the dll limit, which seems to be an intentional Windows design.
Problem: after a certain point (depending on system configuration) it’s not possible to use another unique plugin. There’s a number of (plugin-)dlls that can be handled. Once it’s exceeded, a plugin that is not yet used in the project will refuse to load.
Current workaround: use a plugin that’s already used in that project instead (dll processes are shared with all other instances of that specfic plugin) - here your cpu power is the only limit.
Annoying - happened to me for the first time recently: a project that has worked while mixing had plugins missing on opening another day (without notice). Project sounds different and you might not even realize in the first place, i.e. imagine automated sends that just spit a few words into an FX channel for a delay which is suddenly missing. Spend two days troubleshooting an album mix these days, had to cancel a studio session while musicians were around for a joint finetuning session.
The issue is knows for a while: https://www.steinberg.net/forums/viewtopic.php?f=226&t=95005
It’s not Cubase and not Cubase only (happens as well in other DAWs on Windows) but Cubase needs a way to bypass that limitation.
Until recently it didn’t matter much to me. When that limit was reached it was, well, reached. Irritating but no reason to believe any esoteric xyz-compressor might make a big difference (at an advanced state of a mix where those issues tend to arise) compared to a channelstrip comp or another instance of one used already. No showstopper. The above described behaviour to not load plugins when opening the session again later - though it was possible to insert them while working on the project - was new to me. Re-checking in 8.5 showed the same behaviour. C9 on Windows 7 here, in the other threads on the issue it seems Windows 10 users face the same problem.