Hi there. Same issue here. My iPad mini 2 worked great with a Keystation88 midi keyboard, via USB to lightning generic adapter (not original). iOS was 9.3.x. I moved to another house, so I´ve been several months without using the iPad. When started again using it, I upgraded the iOS as recommended the iPad settings update notifications. And now... the keyboard works just for some seconds (20 or 30 seconds) and it stops with the message "The device is not supported by this iPad", or something like that.
Apple people, please... are you serious? I bought the iPad just for making music purposes... and a simple midi keyboard is not working??!!
And worst of all, it seems apple is not worrying about it, since I´ve read a little above that iOS 11 beta still has this error.