VPP Version: at least since 21.06-rc0~31-g2c1084a69~b496, issue is more frequent with recent revisions

OS version: Ubuntu 20.04

VPP is crashing with some NAT44 tests in CSIT master branch.
Affected are both AVF and VFIO_PCI drivers with TCP and UDP connections

From preliminary investigation this issue appears to be reproductible for any number of configured NAT hosts, however setting lower number of hosts seems to lead to less frequent crashes.
Core dump traceback is provided as an attachment

This issue has not been detected on VPP 21.01

CSIT Ticket: https://jira.fd.io/projects/CSIT/issues/CSIT-1777