I’ve just been having the same issues with Spector and Mystic in a session build on Cubase 8.5 in 2016. It seems this issue is not going away any time soon or if ever, as its clearly been an issue for many many years appearing in Nuendo and Cubase alike.
I agree with the idea of printing these synth patches to audio offered by curteye, very old school, its just sad that this is the only real solution for a consistent sound every time you open that session. I’ve just spent too long rebuilding a session, and having to reverse engineer some patches I didn’t save - very tedious and time consuming - all because of this well documented bug.
To add to the trouble shooting conversation, It seems, that even after a rebuild and save the patches are lost again the next time that file is opened. Furthermore, its consistent across past version of the same session which previously had no issues at all.
Mystic and Spector are great synths with unique sounds to offer but this problem makes them unreliable and as such, unusable if you are looking to reopen a session after its initial build.
Steinberg dev’s please take a look at this issue. In the meantime, you are unnecessarily loosing me to 3rd party synths.