You notice messages in the DL.wlog similar to the following:
'E:\Dell\ArchiveManager\Export\f297edb7-a3cb-b410-5bb2-43f60115abc5.xml' already exists; no need to re-export
Archive Manager is functioning as expected. The File System Data Loader is detecting the same Checksum that it has already processed. You would want to investigate your Exchange Environment, and see if there are any applications queuing the same message and/or Exchange is creating duplicate messages and placing them in the Journal Mailbox. Archive Manager collects the items from the Journal mailbox and places them in the Export folder. Due to duplicate messages in the Journal mailbox, the Dataloader discards the message and a line similar to the Problem Description is logged in the DL.wlog.