Fortigate 200D in HA problem with sync

Hello,

I have couple of 200D in HA mode (active/active), every night they goes "out-of-sync", then in about 30/40 minutes back in "in-sync", I receive message that give me alert. I have this problem every night. I try reboot them but not change. During remain time seems they work fine.

During this time, I receive message that my server behind firewall can't surf on internet.

Have you some idea ?

Thanks

M.