I have the same issue on 2 iPads Air 2 and 1 iPad Pro :(. Crap software, the apple support just told each rime to reset, I did and same thing happens in 2 days. The iPad pro is just 2 months and it is the last iOs device Iever throw money on. Overpriced pieces of crap – phones are deliberately slowed down over time and the software started to have more and more sheety bugs :(.
<Edit: If the dock keeps vanishing from the iPad, this should help temporarily. >