My iPad got updated to 11.3 and I lost the ability to use my usb-midi interface reliably. I had an M-Audio Uno which worked great on 10.3.3. On 11.3 it keeps stopping and a dialog is displayed stating that the "accessory is unsupported".
I think this is related to the M-Audio using more than 100mA. My lightning adapter couldn't inject voltage, so I looked at getting a Bluetooth MIDI adapter.