[MM3-users] Postorius claims 2 messages held when there are none - out of sync

When I view a list via Postorius the "Held Messages" menu item has an inverse-red-"2" next to it, as if there are two held messages. There are, in fact, no messages in "/opt/mailman/mm/var/queue/*" (assuming the held messages should be in "pipeline" subdirectory). When I click on "Held Messages" I get "Something went wrong" followed by "HTTP Error 500: {"title": "500 Internal Server Error"}". How do I fix this?