The earliest recollection of this bug is traced back to PAN-OS 8.1.16 - January 09, 2024. This bug is fixed in PAN-OS versions 9.1.3, 8.1.16. Fixed an issue where both firewalls in an HA active/passive configuration stopped responding at the same time. For more information: https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-16-addressed-issues https://docs.paloaltonetworks.com/pan-os/9-1/pan-os-release-notes/pan-os-9-1-addressed-issues/pan-os-9-1-3-addressed-issues