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.
I ordered an MD-BT01 and of course the iPad could not see the adapter. I was able to see the device on my Android Phone and other Bluetooth devices. I found that you can install the MD-BT01 utility from the App Store, you have to search for MD-BT01, then select Filters and change from iPad only to iPhone only.
After installing that, you can see the adapter but still not use it. I had to install "Yamaha Synth Book" (you also need to filter for iPhone only to install this) and follow the instructions on yamaha's website
After that the adapter works. I haven't received any disconnect messages from the piano after that.