Database locked during cleanup on startup

Sometimes the LibraryScanner thread is not able to access the database when executing the cleanup SQL statements:

Info [Main]: DbConnection - Available drivers for database connections: ("QSQLITE")
Info [Main]: DbConnectionPool - Cloned thread-local database connection "MIXXX-1" QSqlDatabase(driver="QSQLITE", database="/home/uk/.mixxx/mixxxdb.sqlite", host="localhost", port=-1, user="mixxx", open=true)
Info [Main]: MixxxMainWindow - Connecting to database
Info [Main]: MixxxMainWindow - Initializing or upgrading database schema
Info [Main]: SchemaManager - Current database schema is newer at version 30 and backwards compatible with version 28
Debug [Main]: LibraryScanner - Starting thread
Info [Main]: Library - Connecting database
Debug [LibraryScanner 1]: LibraryScanner - Entering thread
Info [LibraryScanner 1]: DbConnectionPool - Cloned thread-local database connection "MIXXX-2" QSqlDatabase(driver="QSQLITE", database="/home/uk/.mixxx/mixxxdb.sqlite", host="localhost", port=-1, user="mixxx", open=true)
Info [LibraryScanner 1]: LibraryScanner - Cleaning up database...
Warning [LibraryScanner 1]: FwdSqlQuery - Failed to execute "delete from LibraryHashes where hash <> 0 and directory_path not in (select directory from track_locations)" : QSqlError("5", "Unable to fetch row", "database is locked")
Warning [LibraryScanner 1]: LibraryScanner - Failed to delete orphaned directory hashes
Info [LibraryScanner 1]: LibraryScanner - Finished database cleanup: 15152 ms
Debug [LibraryScanner 1]: LibraryScanner - Event loop starting
Debug [Main]: Committing transaction on "MIXXX-1" result: true
D

I've only experienced this in a development version yet, never in master or a released version. But now it happened while testing version 2.2.3.