There is nothing in server logs /var/log/messages, mysql.err or mysql.log.
There are some entries in /var/log/apache2/error.log detailing a missing var in the WP theme, but this does not seem related to MySQL backups.
In wp-security-log.txt there is a series of this message: "FAILURE : Error inserting record into wp_aiowps_login_activity." The "Error inserting record" events are recent, occurring today.
- Charlie