Just deployed a new Kemp Load Balancer with a client which promptly broke their cross site DAG.
Usual horrible error:
[PS] C:\Windows\system32>Get-DatabaseAvailabilityGroup -Status
WARNING: Unable to get Primary Active Manager information due to an Active Manager call failure. Error: An Active
Manager operation failed. Error The Microsoft Exchange Replication service may not be running on server XXX-3. Specific
RPC error message: Error 0x6ba (The RPC server is unavailable) from cli_AmGetDeferredRecoveryEntries.
(server xxx-3 is the remote server).
Discovered that the problem was due to an option enabled on the Kemp called Enable Server NAT (SNAT). You can find this under System Configuration, Miscellanious Options, Network Options. Disabling that corrected the issue almost immediately. Seems that the NAT broke the DAG.