802.1x broken in Junos 15.1R5.5

Hello,

we have been upgrading some EX 3300 switches to the recommanded Junos 15.1R5.5 release. Now we are facing the problem that 802.1x isn't working properly anymore. The supplicant messages are send to the RADIUS sever but it looks like the switch drops the response from the RADIUS and uses the server-fail method. Junos 12.3R12.4 showed some random problems too but authentication mostly worked as expected. MAC-RADIUS is not effected.

dot1x {
                authenticator {
                    interface {<ge-*> {                            
                            supplicant multiple;
                            retries 2;
                            quiet-period 10;
                            transmit-period 10;
                            mac-radius;
                            reauthentication 3600;
                            supplicant-timeout 10;
                            server-timeout 10;
                            guest-vlan Guest;
                            server-reject-vlan Guest;
                            server-fail use-cache;
                        }
                    }
                }
}