The earliest recollection of this bug is traced back to PAN-OS 8.1.6 - January 09, 2024. This bug is fixed in PAN-OS versions 8.1.6. Fixed an issue on an HA active/passive configuration where GTP sessions did not properly sync to the passive firewall, which caused a failure on the passive firewall during a failover. For more information: https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-6-addressed-issues