Joplin >= v3.1.4 should allow disabling sync locks in settings, which might fix this particular issue. The 3.1.x versions of Joplin are currently in pre-release.
Instructions for disabling sync locks
(In Joplin 3.1.16/desktop):
- Open settings
- Open the "Synchronization" tab.
- Click "Show advanced settings".
- Uncheck "Enable sync locks".
- Click "OK".
- Restart Joplin using File > Quit.
Screen recording: