I am perplexed.  I have both a 2.4ghz and 5ghz networks set up.  
 

The 2.4ghz does not connect to the internet, but the 5ghz does.  I have IoT devices that only support 2.4 and need to get to the internet.  
 

I cannot use smart mode because I then lose internet for both.  
 

I have done a factory restore and also rebooted my modem. 
 

I have Xfinity with their gateway in bridge mode.  
 

wired connections work great. 
 

any ideas on why this is happening?