@Tony we purchased the router from the UCSD bookstore on 3/4/2015. Guess they sold us a very soon to be obsolete model :( :( tks

@Tony here is where I got the idea that hardware nat might be the problem: https://superuser.com/questions/1170183/archer-c7-ac1750-what-is-the-purpose-of-hardware-nat in the accepted answer point 2:...

@Tony you may not have noticed but it's already at the latest firmware... when this issue first started that's the very first thing I tried. and of course it will work with default settings since...

relevant settings: Allow Guest To Access My Local Network: off Enable Guest Network Bandwidth Control: off Guest Network (2.4G): ON When hardware NAT is enabled guests can reach the WAN but LAN...