Flushed queue Items from the Storage Service DB have been left unattended to for some amount of time and require attention to be imported back.
Periodically, or in reaction to the size of the Storage Service queue, we may purge items from the database, exporting them to the file system in order to ensure performance isn't impacted due to the accumulation of data. These items should be re-imported after the root cause of the accumulation is resolved. Typically this would occur due to an outage of a data storage endpoint (like Exchange), or could be due to a sustained period of high system load. Another cause is that a cmdlet for pool failover or flushing Storage Service was invoked manually and exported files to the file system.
The resource kit tool ImportStorageServiceData is available to import exported items back into the DB for processing.