rax120 in AP mode blocks internet

Hi all,

I recently acquired a RAX120 Nighthawk Router. I set up it in AP Mode behind a Orange Livebox. I need to keed the LiveBox as my main router since my NAS and other decices are connected to It through ethernet.

But devices connected to the AP in Wifi have pb to connect to internet. It seems that the router acts as a "Man In the Middle" which makes the link unsecure. Sonos equipment also can encounter problems. I put an example of connection problem on my iPhone.

The Router firmware is up to date (last firmware version). I made a reboot before posting this problem.

Note that I have a older Netgear R6700V3 which is also configured in AP mode without problem. 

It seems that other prople encounter this kind of problem. It is not clear to me if there is as solution and, if yes, what it is.

BR