I have an Arris NVG599 modem provided by AT&T Uverse (Don't judge me... literally the only broadband provider where I live aside from places like HughesNet). I recently started using the onboard WiFi when my wireless router bit the dust. Plus the Arris has a 5GHz radio where my router didn't.
Anyway, we lost all internet access a little over 2 weeks ago (right before I left for a 2-week business trip). They diagnosed it as a failed router and shipped a new one. Hooked up the new one, still nothing. They sent a tech who didn't touch a thing, and everything mysteriously started working. He was baffled because he saw nothing working then randomly everything started getting access to the web right before his eyes.
All of that may have been irrelevant, but maybe not so I'm including it. While I was out of town, my family was unable to access the web from anything wireless. Everything wireless would connect to the network (and was pingable internally), but got no internet access. Anything wired was fine. I got back into town and found that they had replaced my modem with an older model without a 5GHz radio.
I called Uverse and asked if I could put in the old modem since the replacement was older and wasn't working anyway, thinking the WiFi in the replacement modem was the problem. However, on getting the old modem re-configured after a factory reset, wireless devices still couldn't get to the web.
We set separate SSIDs for the 2.4GHz and 5GHz channels, and I was able to connect to the 5GHz fine with compatible devices. However, devices on the 2.4GHz are still not working. I have another AP in the garage that is also 2.4GHz only, and it is having the same problem. Devices connect, but no internet access. This issue now exists across 3 completely separate devices.
I downloaded a WiFi analyzer app for my phone, and it shows that most of the APs in the range of channels from 6-9. We switched to channel 2 and started getting some results, but it's still really spotty. We got a Kindle and a laptop connected. The Kindle was able to connect to Netflix via the app, but the laptop was getting webpage timeouts. The Chromecast won't connect at all.
May also be worth noting that I have a Corsair Vengeance 2100 wireless headset that uses a 2.4GHz, and it has been having odd "drops" in audio this afternoon as well.
My current theory is that there is something causing interference in the 2.4GHz range. The paranoid in me wants to think it's a jammer, where my more reasonable side is thinking something like oversaturation of the airwaves in my area. But I'm in a somewhat rural community with only about a dozen APs visible if I walk outside, and we only started having this problem within the last 2 weeks or so.