Hi,
I might have experienced a similar bug.
I just spent the whole evening with a friend who has Cubase 9.5 Elements on a Mac.
I choose the HSSE3 as a VST instrument (as rack or as single) and create a MIDI track for it,
I open the plugin UI and try to select patches.
Once I choose a sound for a specific slot it says “loading” and then the slot remains empty and of course no sound comes out.
He was using a Spanish UI, I’ve switched to English UI and when I added a new VST instrument as single (i.e. not as rack), the problem disappeared-
we were able to load problematic projects, select HSSE3 patches where my friend had them blank and it worked fine.
Then we reverted to Spanish UI and the problem came back, and switching to English didn’t fix it this time.
Needless to say, we’ve updated eLicenser, Cubase, HSSE3. Nothing helped.