thank you for your response, many good points.
I guess you’re absolutely right, Thunderbolt shouldn’t add any significant latency. But perhaps in heavily encrypted file systems on an external SSDs this might still apply, at least to a certain extent (might actually be interesting to find out by really measuring the data transfer time, IF one had the necessary electronics lab resources).
After looking into the Steinberg help section (had never read that before myself, so until now I was clearly just speculating - please forgive me), I found this:
the whole process of registering / moving content libraries seems to be pretty much the same on both platforms:
Manually Installing Libraries
This was also the first time I actually looked up where Steinberg Library Manager stores its path data, registered content file names and IDs , and it’s not even a real database file like with the MediaBay, but just a slightly larger XML file named “ContentManager.xml”, which resides inside the same Cubase settings folder where all the other XML files reside. This is what a simple Library Manager entry looks like, in Windows 10 - the content package is called “Colliding Worlds”, categorized under “Groove Agent” (I’d just replicated the category tab names in Library Manager as separate folders):
So, when looking into the three relevant places inside the Windows registry, I found lots of empty key folders, so my conclusion is that Steinberg nowadays seem to rather put any presets inside XML files, which makes it much easier to search for possible errors (if they occur, that is).
Now I still don’t have any idea why you had that strange effect… something with the user rights perhaps? Maybe we’ll find out, once you’ve tried to register your copied content files.