Some time back I encountered an issue, where Availability Group Disappeared from the management studio after multiple unplanned restarts of nodes of Always-On Cluster. In most of the situation you will end up in a state where you AG group will stuck in resolving state, which can be easily handled. During investigation it is found that the Always-On cluster was configured with multi-subnet cluster and has issues in reaching the third node, also the quorum was not configured properly.

Error Message: The local replica of availability group ‘MNREGA_PRODAG’ is being removed. The instance of SQL Server failed to validate the integrity of the availability group configuration in the Windows Server Failover Clustering (WSFC) store. This is expected if the availability group has been removed from another instance of SQL Server. This is an informational message only. No user action is required.

Why did my replica disappear?

As a clustered resource, the availability group state information is stored and maintained in the Windows Cluster store. SQL Server must be able to communicate and access the availability replica’s state information using Windows cluster protocol. SQL Server will drop a replica if it tries to read the replica information from the cluster store (registry) and one of the following conditions occurs:

• SQL queried the cluster store successfully and the replica did not exist – then SQL Server will drop the replica
• SQL queried the cluster store successfully and the replica was found, but the data was corrupt
• SQL queried the cluster store unsuccessfully

If one of these conditions occurs, the replica may be removed. This behavior is by design but should be very uncommon and may signify a problem with Windows Cluster responsiveness and warrants further investigation.