There’s a problem with somewhat similar symptoms that was being chased in Error “database is locked” when trying to run a backup after a force stop #3445 for awhile, and was mentioned in Restore fails with “Failed to connect: The database file is locked database is locked” although there was concern over version difference @mikaelmello did a historical version test for the GitHub issue and thought that the issue arrived in 2.0.3.6. While I wouldn’t suggest doing this in anything but a test environment, testing the issue in 2.0.3.3 and 2.0.3.6 might give some clue as to whether these problems are related, or maybe someone else will offer their guess.