You coud log into the CLI and submit "show stat virtual-sensor | beg Per-Signature" and see what signatures might be triggering. Do this for a few times over a period of 20 minutes to get a baseline on what signatures regularly fire/increment. Then perform another copy between Unix machines, submit the above command again and see what signatures trigger to see if you can find one, or more of them that might be causing your issue.
You could also try creating a filter to remove all signature actions on SCP traffic between the affected machines to see if that would help.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...