It seems that the AbstractDatabaseManager behavior is now to close the connection after the buffer is flushed (or immediately after a write if there is no buffer). These are the calls to commitAndClose().
The intended behavior for close() is that it would return a connection to the connection pool. That would make sense for most good database drivers.
However, the MongoDBProvider simply closes the MongoClient, releasing the entire pool. This means that further attempts to write to the log, after the first time, will fail.