I made a folder called VSTsound on another hard-disk partition, in my case F:\VSTsound.
Then moved all the large ***.vstsound i found in C:\Users\Administrator\AppData\Roaming\Steinberg\Content, also those from the subfolders like Halion, Groove Agent etct, and eventual other possible places (do a search?) on C, all in to same directory to the new folder F:/VSTsound.
In the NEW folder i created shortcuts for all those collected ***.vstsound files. Then i moved the shortcuts back to C:\Users\Administrator\AppData\Roaming\Steinberg\Content.
Never had an issue since. If you still have problems, you could create a subfolder in there, with names like C:\Users\Administrator\AppData\Roaming\Steinberg\Content\Groove Agent\VSTsound, and just put a copy of all the shortcuts there too if you like.
You could try to use the Steinberg library manager, but IMO it makes too many errors deleting the wrong files. F
(PS i want to sell my Cubase 9.5 pro retail, or a full Cubase 10 PRO retail, i have both) And if someone makes a right offer, i can include licenses for Halion 5 and or Simon Phillips Studio Drums on the eLicenser. PM me then, paypal and buyers warranty is possible)