From the Palo Alto documentation below, "when a VPN is terminated on a Palo Alto firewall HA pair, not all IPSEC related information is synchronized between the firewalls... This is an expected behavior. IKE phase 1 SA information is NOT synchronized between the HA firewalls."
And from the second link, "Data link (HA2) is used to sync sessions, forwarding tables, IPSec security associations, and ARP tables between firewalls in the HA pair. Data flow on the HA2 link is always unidirectional (except for the HA2 keep-alive). It flows from the active firewall to the passive firewall."
https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA14u000000HAuZCAW
https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA14u000000HAuZCAW&
&lang=en_US%E2%80%A9
lang=en_US%E2%80%A9&
&refURL=http%3A%2F%2Fknowledgebase.paloaltonetworks.com%2FKCSArticleDetail
refURL=http%3A%2F%2Fknowledgebase.paloaltonetworks.com%2FKCSArticleDetail
https://help.aryaka.com/display/public/KNOW/Palo+Alto+Networks+NFV+Technical+Brief

Reference:
https://live.paloaltonetworks.com/t5/Learning-Articles/Packet-Flow-Sequence-in-PAN-OS/ta-p/56081

You are unable to downgrade from PAN-OS 8.1 to an earlier PAN-OS release if variables are used in your template or template stack configuration. Variables must be removed from the template and template stack configuration to downgrade.