Admins Handbook

If your replicated databaces is susspended or failed you may need to reeseed them.

Check status:
Get-MailboxDatabaseCopyStatus -server MyExchange

Reseed:
Update-MailboxDatabaseCopy DatabaseName\ReplicaServerName -SourceServer ActiveServerName -DeleteExistingFiles:$True
ReplicaServerName is the server with the FAILED copy.

Id Content index is in failed:
Update-MailboxDatabaseCopy -Identity DatabaseName\ReplicaServerName’ –CatalogOnly”