The following error may be seen when importing data into Enterprise Vault:
Vault Store [Name-of-VaultStore] is in Backup Mode.
Additionally you can check which vault store is in Backup Mode in Manage & Operations > System Health > Storage Paths

The items should be reprocessed after the Vault Store comes out of backup mode.
If Vault store is in backup mode for unreasonable time follow instructions in the article below:

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