Upload hangs on "Score is being processed"

See:
https://musescore.com/groups/improving-musescore-com/discuss/5049539
and
https://musescore.org/en/node/295546
or
https://musescore.com/user/11758031/scores/5759953

Applies to most score files. On rare occasions upload goes through after several minutes, sometimes it just hangs forever. One time it stopped after several hours but the score was then "not found" when selecting it among "my scores" on the web.
Applies to uploads using the Musescore webpage interface.
Applies to uploads using the Musescore windows application (ver 3.2.3.7635, have not tried other versions).