iPhone6+ 128G iOS 8.0.2 (same issue under 8.0.0)
My 2.4GHz G network (WPA2) would work fine for a few hours, then go into disconnect mode. Trying to reconnect it tells me the password is invalid. Every other wireless device connects with that password (cut/paste - no typo). 2.4GHz quits working on the iPhone6+.
I even tried changing the password to '12345678' and everything connected but the iPhone6+.
Interestingly, the 5GHz N network I also have works fine on the iPhone6+. No issues with that one. But my house is running G repeaters, so I really need that band to work. Plus most of the public network will be G. And as I said everything else works but the iPhone6+.
I've reloaded the phone twice (that's another disaster for telling around a campfile.) I've reset the network many times. At certain points in the day, the SSIDs will disappear, then mysteriously reappear later on.
Last night I connected at a friend's house (G). Two hours later I was at the girlfriend's house and it said I was still connected to the WiFi 20 miles away.
I had a talk yesterday with a level-2 tech at Apple. He swore I had my network set up wrong. *sigh* After a quick chat explaining my credentials he's expediting a replacement phone to me for Monday. I'm hoping this fixes the issue. I believe it's hardware, as 8.0.0 works just fine on my iPhone5 and iPad3 (both 8.0.0), but not the iPhone6+.
I'm open for help, this has made the rest of my hair start falling out.