It is very annoying that the G3100 router does not have Hairpin NAT (NAT loopback) enabled. This is a common feature found on almost all routers including the G1100.
Hairpin NAT says that if I use the external IP to access the router from inside the LAN, then it should behave the same as if I had accessed the router from outside the LAN. That means apply the port forwarding and mapping to the request.
This is very annoying to me because I have an app on my phone that uses the external name for my network. This app works fine outside of the house. When I am inside the house the phone switches onto wifi. This causes the mobile app to stop working. Why? Because the mobile app is using the external name for the router and it is expecting port 443 to get forwarded. Since the G3100 does not have Hairpin NAT enabled the ports don't get forwarded and the app stops working.
This should not be happening. My mobile app should work the same whether it is external or internal to the network. Please enable this feature on the G3100.
Reading around the forum I see other people experiencing similar issues without knowing what caused the problem.
Edit: I got my app working by moving to another port. Reddit post clued me into Hairpin NAT works on ports besides 80/443 on G3100.