Failing EAP-TLS authentication on mobile phones with FreeRADIUS

I would like to automatically connect our iPhones to the network using a RADIUS server and EAP-TLS. I use an MDM solution named Baramundi to deploy the configuration and the certificates to the devices. The RADIUS server I am using is FreeRADIUS. When watching the traffic between the authenticator and the RADIUS server by running the RADIUS server in debug mode, I see that the communication suddenly stops after four packets transmitted. The last line I see in the RADIUS log is an Access-Challenge packet sent from the RADIUS server to the authenticator / supplicant and then, there's no packet s

Question by TomS on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.