I recently updated a ProFTPD at version 1.3.2a to 1.3.3c and realized that failed logging of actions will now quit the FTP connections.
This is related to the statements
In previous versions it was not necessary that the
SQLNamedQuery will work,
but now the connection will close, if the query fails.
The solution is to disable the statements
SQLNamedQuery, if you can’t provide a working query or you no longer want to.
In my environment the logging was probably filling a huge table
action_log and someone dropped that table in the past to free space on
the MySQL instance, perhaps in the middle of the night while fixing capacity
problems on that web server.