The earliest recollection of this bug is traced back to PAN-OS 8.1.20 - January 09, 2024. This bug is fixed in PAN-OS versions 8.1.20. Fixed an issue where the SYN-ACK packet matched stale entries in the session flow table and was dropped on the firewall with the following error message: Inactive flow state 0 . For more information: https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-20-addressed-issues