I've been using this router for sometime w/o issues.  in the last day or so, the guest wifi drops out.  it is broadcasting ssid and you can connect but you cannot get to the internet.  I've not changed any settings - so "it used to work fine, and nothing has changed but now it doesn't". 

rebooting the AD7200 will bring it back to normal and then after a seeming random but shorter that 60 minutes the problem is back.