Since the default value of call_screen_fkeys_on_connected is changed: the F_REC is now removed by default because not used by many PBXs.

If you need to have the F_REC key back you should configure the call_screen_fkeys_on_connected with the value: F_LEFT F_RIGHT F_DUAL_AUDIO(not:Conference) F_REC(not:Conference) F_DIALOG(not:Conference) F_CONF_ON.

The setting call_screen_fkeys_on_connected isn't managed by the web interface, so you have to configure it via provisioning or via HTTP request.