this is mentioned in 8.1.9 PAN OS as addressed issue.
Please find the detail:
Fixed an issue on a firewall in a high availability (HA) active/passive configuration where HA1 and HA2 links stopped passing packets, which caused a split-brain condition after an automatic configuration sync.
I need information if this is related to any particular hardware model. also if FWs in HA are already running fine on 8.1.7 or 8.1.8 or prior to this, will they get hit anytime ?, or only if they upgrade to lower version than 8.1.9.
This issue is addressed in PAN-OS 8.1.9, this means you will need to upgrade your firewalls to PAN-OS 8.1.9 or higher to prevent (or fix) this issue from happening
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