5 Ghz wifi network drops/disappears frequently

Got a new Nighthawk X4 C7500 a few weeks ago to use with my Comcast Xfinity service. For about the first week, it worked great- no issues. For the last 2 weeks or so, several times a day either the 2.4 ghz or 5 ghz wifi network will drop its connection on all devices. It's primarily the 5 ghz, but occassionally the 2.4 ghz won't connect either (sometimes both don't work simultaneously, sometimes 1 of them will be available). Sometimes the network won't display at all in the available networks list of my devices, and sometimes it will display and connect, but will say there is no internet. This is on a variety of devices: phones, TVs, speakers, etc. And I know it's not a router placement issue because when the 5 ghz network is working, the connection is very strong/fast throughout my house. Also, the network still won't show up as available sometimes when my device is 2 feet from the router. And I am the only network on the channel. Does anyone have any advice? It would be greatly appreciated.