Synchronization does not copy all documents to target. You have ran a synchronization previously and have deleted documents from the target file cabinet.

When you delete the synced documents, the database entry of these documents are moved to the FileCabinetName_DEL table. This prevents these particular documents from processing again.
We would need to delete all entries from the FileCabinetName_DEL table, then run the synchronization job and all documents will successfully copy over to the target cabinet.

KBA applicable for On-premise Organizations ONLY.