If a hidden folder exists in the Domino mail file, the Domino Mailbox Archiving Task stops archiving of that specific mail file and no other items are archived.
Source: Enterprise Vault
Category: Lotus Domino Mailbox Archiving Task
Description: There was an error processing a mailbox. The task will process the mailbox again on the next archiving run.
Task: Domino Mailbox Archiving Task
Error: Folder [Hidden Test Folder] does not exist.