Problem Captive portal with facebook Authentication

Hello guys!

Our guest network with captive portal redirected to our fortiautenticator if I log-in with facebook authentication the page to enter the username and password the page appears as text only.

here is the screen of the page

i use FortiAuthenticator v6.0.2, build0041 (GA) and Fortigate 100E v6.2.3 build1066 (GA)

thanks for your help

Bye Bye