R6400 Router 2.4ghz not working, but 5ghz is fine

Exact same problem.  Had the router for about a year and no problems. Yesteday the 2.4ghz stopped working.  While doing my own initial trouble shooting, I updated the firmware (hoping that was the issue) to 1.0.1.20 and that didn't fix it.  All of my devices can see it (mac, pc, iPhone, XBox, HP printer), but not connect (won't resolve an IP address).  All of the 5ghz capable devices work just fine on the 5ghz network.  I've read most of R7000 thread and have done the factory resets, manually entered all settings again, used the reset button on the back, used the WiFi button on top, tried the guest 2.4ghz network (didn't work), dropped the speed to 54Mbps, tried all the manual channels, tried using no security encryption.  NOTHING WORKS.