Recently we got the issue from customer, they failed to add the database into the existing AG with error 988:
Msg 988, Level 14, State 1, Line 17
Unable to access database ‘ag_03’ because it lacks a quorum of nodes for high availability. Try the operation again later.
No backup and no restored happened on all nodes.
Based on this message , usually we will check SQL Server errorlog, cluster log , run cluster validation to confirm the current cluster healthy. But on this issue, the root cause is not caused by the cluster issue.