The MonitoringGroup settings can't be used reliably to make sure the CAS monitoring mailboxes can be created as expected if the organization has more than 11 DAGs in Microsoft Exchange Server 2019 or Exchange Server 2016.
To fix this issue, install one of the following updates:
Note: After installing the update, you need to run the following cmdlet to enable the feature:
Add-GlobalMonitoringOverride -Identity Monitoring\Configuration -ItemType Maintenance -PropertyName EnableIterateAllDags -PropertyValue true
Learn about the terminology that Microsoft uses to describe software updates.