Your NAT type is likely set to strict because of configured setting on your router or firewall. To change this, you must enable post forwarding or use a VPN service to route traffic through another server. This should help open the ports and resolve the strict NAT Type. The only difference to STRICT to OPEN is that lobbies you wont be host but it doesnt effect your game play in any sort of way.
Also i would recommend making sure that you have toggled UPnp to ON.
Steps on how to change on xbox settings;
Head to "settings", go to "network settings or advanced settings" go to your router and enable UPnp.
