Client looses connection to guest ssid after leaving wlan and rejoining

Hello,

we have problems with clients, using a guest ssid with a captive portal via fortiauthenticator. When the clients connect to the ssid the first time, he is forwarded to the captive portal and after agreeing the policy, it is able to browse the web.

When the client is disconnected from the wifi, for example, when leaving the building, the client can´t reconnect to the ssid, until the ssid is completly deleted on the client site. Only when deleting the ssid, the client is able to reconnect to the ssid.

FortiOS 6.0.4

FAC 5.5 and 6.0

Thanks for your help