Does not support a true bridge or passthrough mode. Dmz of your asus ip is the closest it offers. I ran into this recently at a customer site and found running the at&t as a normal router and port forwarding
blue iris port to the asus address behind it, and port forwarding in the asus to the blue iris pc was the most reliable and fast access when a vpn is not an option. Your pace at&t router is causing your issues in current configuration. It will be double nat the way I described, but it does work.