The earliest recollection of this bug is traced back to PAN-OS 9.1.3 - July 29, 2024. This bug is fixed in PAN-OS versions 9.1.3. ( VM-Series firewalls only ) Fixed connection issues between IPv6 peers when the IPv6 neighbor cache was synchronized in an HA cluster where, after failover, the newly active firewall did not send multicast neighbor solicitation from its global unicast address. For more information: 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