The earliest recollection of this bug is traced back to PAN-OS 8.1.9 - January 08, 2024. This bug is fixed in PAN-OS versions 8.1.9. Fixed an issue where an out-of-memory condition caused all IPSec tunnels (which includes IKEv1, IKEv2, and NAT-T) to stop responding. For more information: https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-release-notes/pan-os-8-1-addressed-issues/pan-os-8-1-9-addressed-issues