The disk space is running low.
The Project Setup Station shows a large number of batches with an "Out of processing" status if the working batches filter has the "Show out-of-processing" option enabled.
Processed batches are set to be removed automatically after a certain period.
The batch gets the "Out of processing" status when all the documents are removed from the batch. This may happen if documents are deleted during the Verification.
The batches that already have "Out of processing" status have to be removed manually. But to prevent new batches from piling up, verification operators may send unneeded documents to the Processed stage instead of deleting them.
To allow sending the batch to a Processed workflow stage, uncheck the "Linked to previous" option for a Processed workflow stage.
To send unneeded documents to the Processed stage from the Verification, navigate to Task > Send to > Stage > Processed.
The same can be done from the Web Verification Station: