I have an iPad Air 2 which was locked due to a pupil putting the incorrect password in too often. I tried numerous times to recover it but it always told me that it could not be detected. After reading all your comments above I decided to contact Apple but needed as much information about the device as possible so kept putting it into recovery mode so that I could get the serial number etc off of iTunes.
As if by a miracle after starting the recovery session for a third time it decided to recover. I wasn’t able to restore the previous settings as they were probably never saved to iTunes or iCloud, but at least I now have a functioning iPad.