This means that the firewall does not have a mechanism to monitor the status of the IPSec VPN tunnel and generate logs when it goes down or up. The Tunnel Monitor is an optional feature that can be enabled on each IPSec tunnel interface and it uses ICMP probes to check the connectivity of the tunnel peer. If the firewall does not receive a response from the peer after a specified number of retries, it marks the tunnel as down and logs an event1.

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&lang=en_US%E2%80%A9&refURL=http%3A%2F%2Fknowledgebase.paloaltonetworks.com%2FKCSArticleDetail

https://docs.paloaltonetworks.com/pan-os/10-2/pan-os-admin/high-availability/set-up-activepassive-ha/configure-activepassive-ha In an A/P HA pair, HA (High Availability) timers are used to determine how quickly the firewall should fail over in case of a failure. Typically, the firewall administrator can choose between several predefined timer profiles such as "normal", "aggressive", and "fast".
Changing the HA timer profile to "user-defined" and manually setting the timers would allow the administrator to fine-tune the failover timing and make sure it meets the uptime requirements for the critical business applications. This approach allows the administrator to set the timers to the lowest possible value without compromising the stability and security of the firewall.

When deploying SSL Forward Proxy decryption, a forward trust certificate must have a subject alternative name (SAN) and be a server certificate. SAN is an extension to the X.509 standard that allows multiple domain names to be protected by a single SSL/TLS certificate. It is used to identify the domain names or IP addresses that the certificate should be valid for. A private key is also required but it is not mentioned in the options. A certificate authority (CA) certificate is not required as the forward trust certificate itself is a CA certificate.

NAT oversubscription is a feature that allows you to reuse a translated IP address and port for multiple source devices. This can help you conserve public IP addresses and increase the number of sessions that can be translated by a NAT rule.