I have exactly the same problem which is described in this discussion.
Model: iPad Air 2 Cellular (64 GB, space gray, iOS 8.1.2)
Production week: 49 (December)
Factory: DM (China - Foxconn)
Provider: T-Mobile Germany
After I had dispatched it to Apple for repair via Apple Support Apple sent it back to me and said that my iPad works correctly. They didn’t give me a exchange device.
I don’t what’s up at Apple but the whole story is a mess.
1. Apple should officially admit that they have a problem with Apple iPad Air 2 und should give the customers am small report about the current results.
2. Apple iPad Air 2 is a premium device. The customers exspect high quality. This is one problem of many (https://discussions.apple.com/thread/6538224).
My opinion, don’t buy Apple products at present. First they have to learn how to handle correctly with customers.