Nintendo Switch error code 2618-0513 on 5G Gateway G4SE

I've recently updated my router to the 5G gateway G4SE. I am trying to do online play on Mario Kart 8 Deluxe and it gives me the error code on not being able to connect to other consoles. I haven't had much of a problem with my old T-Mobile router and I've tried all other options of restarting my router and making a new  network with a different WPA than my main network. I've contacted Nintendo about this and they have said to restart my router and try again and also that it may be a firmware issue. My firmware on my router is 1.03.20 which I believe is the most recent one. I only had problems with this certain game and online play. What solutions can I do about this ?