I've encountered issue when sending ICMP ping to between hosts when sending through Site-to-site IPSec tunnel. Pings works for 5 minutes and then it stop working for few minutes.
Here is the output of fw zdebug drop when pings stop working:
;[cpu_1];[fw4_0];fw_log_drop_conn: Packet <dir 1, x.x.x.x:1285 -> y.y.y.y:0 IPP 1>, dropped by do_outbound, Reason: encryption failed;
Other traffic like SSH, VMWare VDP backups works without any issue.
I couldn't find any Secure knowledge regarding this issue, any pointers for further analysis?