Problem with gigaset A510 IP. Sometimes ping unreachable.

Hello,

OS: 6.28
Firmware: 3.22
Model: 2011UiAS-2HnD

My connection:

fortigate 100d (public IP) → VPN IPsec → Ubiquiti (I don’t have access - public IP) → forward ports ipsec vpn → MT (connection VPN IPsec)


When I try to ping from behind the FG to Gigaset which is connected to MT, I have a break in the table.

When is still Tools → Ping from MT to Gigaset, then my ping from behind the FG to Gigaset there is no break.

Please help me.