Your use of the nat 0 command created a dynamin no-nat entry that is created when traffic is sent from inside to out. Translations timeout when no traffic is sent from the inside host for the configured time period, thus making the host unavailable. When you would ping out, the translation was built again.
You can accomplish this with Nat 0 using an ACL. Nat 0 commands using ACLs also make permanent entries in the translation table.
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...