Fotrigate 901G_WAN port led blinking Green and Static Orange

Hello,

i have a fortigate 901G and connected to old isp modem with vlan subinterface and do static route to the next hop ip,

WAN port led blinking Green and Static Orange, So :

i created also loopback interface on foritgate and configure it with public ip and ping from this ip to 8.8.8.8 the ping is not compeleted with 100% many times give me loss with 20% and 40% and 80%

a tried to change port speed to 100Full Duplex from 1000 auto nego. and it is still lossing the packets ping and user not able to connect to internet or ping 

- So is there is any recommendations from you to solve this problem .