when you turn your modem firewall off, at that point your devices will rely on their firewall, and devices that don't have one will have security risks. btw, if you have port forwarding rules that use the same port (forwarding the same port to 2 different devices). it won't work
Could you take a screenshot of the port forwarding thing. And censor any mac address or public ip. Your private ip doesn't need to be censored
Oh wait.... In the wan connection list, try changing it to INTERNET something. Keep changing it until one of them works Also rebooting the router would be recommended