So I could authenticate normally to the wifi network but then it pushed me to this log on page (for what reason I have no idea). I wanted to connect to the internal wifi to stream music to a wired network device and dont know why I was being prompted with this Asus page.
Asus did some iOS-related fixes about Internet detection with 22.214.171.124.266 (only available for the RT-AC66U at this time). You could try my firmware for the RT-N66U, which also includes those iOS fixes they did.
Asuswrt-Merlin: Customized firmware for Asus routers Github: github.com/RMerl - Twitter: RMerlinDev
See the sticky post for more info.