Since the reorganization of base content I sometimes get similar issues.
In Dorico I need to install a special instrument table to get it working again.
I’d kept a copy of Sonic SE 3 on the system for the sake of hosts that cannot run VST3. It is almost unusable now. The General MIDI portion is seriously borked. Oh well, I plan to just remove it and use bidule to bridge Sonic or HALion 7 to those old hosts.
Aside from HSSE 3 or older being seriously broken if the ‘newest set of base content’ is installed…it seemed to help if I just launched a stand alone instance of HALion and Sonic, and just let them sit there for a while. As in, launch them, and go out to lunch.
Theory being…whatever database and such that Steinberg is using these days gets time to ‘build/rebuild’ in the background?
Seems to have helped in my case. I’m getting all the instruments I should get. I did notice that sometimes I need to clear/reset the filters! There is an option in Sonic and HALion that automatically syncs filters with the selected instrument slot, or something like that.
Give it a toggle and see if it helps.