Adding yet another example of this issue!
Yep I have had the same issues with WiFi.
I don't want to switch off the 5Ghz because of other devices tat use it, so I can't say if that was the problem, but I do have two identical iPad Air's and both updated, one has no problems, the other has been rendered almost useless with this problem. I thought perhaps it was some sort of conflict with other apps but having done a full restore on the faulty iPad the problem still remains... At a loss to understand this I have reverted this one back to iOS 7. Disappointed! I've never had to do that before, and I've had many many 'I' devices since my first iPod in 2001 (still works quite well!)
I expect a fix pretty soon.