https://support.microsoft.com/en-us/topic/kb3213703-fix-an-always-on-secondary-replica-goes-into-a-disconnecting-state-10131118-b63a-f49f-b140-907f77774dc2
KB3213703 - FIX: An Always On secondary replica goes into a disconnecting state - Microsoft Support
Fixes a problem in which an Always On secondary replica goes into a disconnecting state.