Hi @michael lustig ,
I did some search about your error message and found some similar threads. In most of them, seems the Network settings might be the key point. So, I would suggest you to check the Network settings of your DAG by running the command like below:
Get-DatabaseAvailabilityGroupNetwork | FL
For more information:
Get-DatabaseAvailabilityGroupNetwork
After installing Excange CU18, two database passive copy is disconnected and failed state
Hope these could help.
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