That means the ASA does not find the matching connection entry for that particular SSH traffic.
A couple of reason why we can see that log:
1) ASA already closes down the connection base on the idle timeout, and when the application sends a RST packet, ASA does not have that connection entry anymore, hence the syslog message. This is normal.
2) ASA has an existing new connection for SSH, however, the application itself is sending a RST for previous connection. This is also normal.
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...