Hello vikassingh,
1. The ScreenOS version is 6.3.0r13.0. The peer device is Palo Alto PA-820. Is there any list show which firewall support VPN monitoring with Juniper firewall?
2. I've no idea about ESP packet. Do I need to use Wireshark to capture them?
3. Continue ping between 2 firewalls without drop (very stable), even VPN monitoring was enabled. It start up and down when there is no traffic. I'd enable "Optimized" and "Rekey".