Hi,
the query used in the mssql plugin to report the latest backups (file "last.backup.get.sql"), is not optimized. 
It can take several seconds(/minutes) to run on Alwayson clusters having many databases and availability groups.

The "NOT IN" can cause problems if NULL appears. It is advisable to replace it with a "LEFT JOIN ... WHERE IS NULL", which is more efficient and secure.

Attached is an optimization of this request. The result is instantaneous.

Best Regards

Sébastien