MS support told me, the fix will be released in SQL Server 2019 CU6, only if you enable a support flag, you'll get the log messages

I have a case ongoing and MS said:

....

Thank you for your patience, we have an update on this case. Our Product team is going to release a hotfix in near...

I did a fresh installation of SQL 2016 SP2 with 2 Cluster Nodes and 12 databases in the AG. It all worked fine without any "UpdateHadronTruncationLsn" message until I did...

I get the message "UpdateHadronTruncationLsn(8) (force=0): Primary: 0:0:0 Secondary: 37:336:1 Partial Quorum : 0:0:0 Aggregation: 37:336:1 Persistent: 37:336:1" exactly each 30 minutes.

I do have some other AON installations which work...