Demoing Cubase 11 on macOS and noticed MediaBay would get stuck scanning my sample library. I found that it was getting stuck on a midi file with a backspace in the filename and a folder alias that was inside one sample pack and rather than flag them it would just scan endlessly.
I assume there are a myriad of reasons why MediaBay might get stuck scanning but in my case fixing these two files removed some of the issues. Perhaps someone else may find that useful.