On my system the Groove Agent 4.2.30 is extremely slow to show the MediaBay results. And even not showing anything at all in the MediaBay window. After clicking “Rescan Disk” it takes very long time to rescan and with inadequate results. This goes for all sets as well as for individual sets. This goes for the stand-alone version and the VST version in Cubase Pro 8.5.20
I have the same setup on Windows 10 and everything works fast and smooth there.
I have tried the HALion 5 MediaBay and everything is fine there - it’s fast. 
Everything on my system is up to date.
Solved
I deleted HALion 5 mediabay3.db file
Location: Macintosh HD/User/username/Library/Preferences/HALion 5/mediabay3.db