I was able to get the guest network setup using my phone and the ASUS app. The app seems to be a bit more robust lately, not sure of there was a big update but everything seems to be working now. You just need to use the phone app to get the guest network setup...
yes, new firmware 382_51640 and a factory reset
Correction: No, After FW and reset, and in order to fix a problem I have been working on for the last several days HERE I had to use a MAC Clone address. That is the only way I have been able to solve the above problem. Is that causing the guest...
I signed up just to post this. I tried all the solutions in the previous posts to no avail. What worked for me is switching IPv6 to Passthrough and then hitting the MAC clone button under the WAN settings. Extend the TTL = Yes, Spoof LAN TTL =Yes. Reboot and connected.