iOS 8 5GHz WiFi issues

You nailed it Roger; iPad4 wouldn't connect to 5GHz no matter what I tried until I switched my router from Ch140 to Ch44. As soon as I went back to Ch140 iPad4 dropped the connection and I reconnected immediately when I switched back to Ch44. Many thanks.

Alkaline: Thank you! Changing my channel selection on the router (to non DFS channel 48) didn't help until I 'forgot' my network & logged back in. Perfect now!

Roger Wilmut1 Thank you! Changing my channel selection on the router (to non DFS channel 48) initially didn't help, but once I 'forgot' my existing network in my phone & logged back into the SSID - my connection now works. Perfect!

iPhone 5Ghz wifi connection issue fixed (aka "wifi password incorrect" error)

We have 6 iPhones in our household and all bar 1 of them connect to the wifi network without problems. One of them (an iPhone 5s) only connects to the wireless 5G network. It will connect to the 2.4G wireless when it is physically next to the internet router (not much good for wireless).

I happened to upgrade my router firmware to the opensource DD-WRT firmware and I played about with the settings on the router which caused the problem iPhone to stop connecting to 5G as well. It saw the wifi network okay but when I tried to join it, it just showed the "wifi password incorrect" error message. It seems that this iPhone has a wifi signal problem (probably hardware related) and can only connect when the signal is of a certain strength and quality. Which explains why it only works on some wifi networks.

To fix the iPhone 5s so that it connected again to the router I changed the router wireless settings for the 5Ghz band so that the "Channel Width" is set to "Full (20Mhz)".

This cured the problem at home, unfortunately it didn't improve the 2.4Ghz connection issue but that might be peculiar to my iPhone.

Hope this helps others as it took me ages to find this out.