FYI, in 0.53 same issues are there.
In addition ( or i just didn’t notice before), the browsing local files by Folder does not work correctly.
I put some folders mit Mp3s in the MusicBox directory (so not on USB). In the web interface I saw the folders but only the first folder showed any contents. Mopidy log did not show any error and a correct number of files scanned during startup.
Running
pip install --upgrade Mopidy-Local-SQLite
updates the extension from version 0.8.1 to 0.9.2 which resolves the issues.