Always On issue due to that backup getting fail with below error.

Actual Error:  Due to that backup getting fail

Issue: FULL/Diff/Log backup Job are failing due to below error.

Cause: If a WSFC cluster is destroyed, it removes all registry keys related to Always On Availability Groups.

Solutions:

Solution 1 – Completing replica set up, or removing secondary replica: This can be a very simple problem, however the error does not really point you in the right direction. If you have not completed the setup of the database on your replica(s) you might get this error. To resolve either complete setup or remove the replicas from the availability group.

Solution 2 – Take resource offline and then bring back online: Self-explanatory, try taking the resource offline or fail it to another node and then fail it back.

Solution 3 – Restart the node: If you still haven’t resolved it with the prior solutions restart the node.

Solution 4 – Remove HA and Re add:Hopefully you don’t have to do this. But as per Microsoft the only solution I have left for you is to remove all your HA replicas and AG groups and then untick the Availability Group feature in SQL Configuration manager. Restart SQL and then add the feature back again. As per the article you may need to do this on every node.

Impact: User might not able to access the database.