If MythTV is not scheduling recordings, tail -f /var/log/mythtv/mythbackend.log while running mythfilldatabase. At the end of it's run, mythfilldatabase will trigger a re-scan of upcoming recordings. If an SQL error occurs, it will be shown in the log.

"Prepared statement needs to be re-prepared" appears to be a MySQL error. This was fixed with mysqlcheck -u mythtv -p --repair mythconverg (using the password from /etc/mythtv/mysql.txt ). Rescheduling appears to happen immediately, without running mythfilldatabase again.