iOS 8 and iOS 8.0.1 both have a lot of "problems".
The iOS 8 version is not really smooth, the number of complaints is getting bigger and bigger; If the 3G or Wifi connection fails, your phone becomes "useless" somewhat, because today, "online" seems to be often and more often than ever. To fix it, you should do a few basic steps:
Step 1: Reset network settings : go to Settings , select General , select Reset, select Reset Network Setting (picture below)
Step 2: Next go to Settings , select Privacy , select Location Services , select System Services then turn off ( turn off) Wi-Fi Networking.
Step 3: Finally reboot the device, after the device reboots you try to reconnect to the Wifi network and imagine the result. Of course this is only a temporary "wait and see" measure while waiting for Apple to release an official patch update for all iOS8 devices, noting that this problem of Wifi connection does not affect duo iPhone 6 and 6 Plus.