Symptoms
Group metrics generation does not work in a multidomain environment, and Microsoft Exchange Server can't update the msExchGroupMemberCount and msExchGroupExternalMemberCount attributes.
Resolution
To fix this issue, install the following updates, as appropriate:
Cumulative Update 12 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019
Cumulative Update 23 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016