Today I'm faced again with Failed Index State on databases in DAG, so they couldn't copy and switch properly.
1.Add Universal Security Group ContentSubmitters
2.Assign Full Control access for:
3.Check database file path on one or ALL Mailbox Server's. You could do this by EAC or EMS. Below the gui version (EAC):
4. Go to the database path and select Folder with GUID in the name. Example - see below:
5. Stop search services: Exchange Search and Search Host Controller :
6. Delete folder or folders with GUID in the name on mailbox server/serverss
7. Start search services.
8. Wait until indexing is finished.