Lightning to USB3 Camera Adaptor not supporting all-Apple audio

I’m running Simply Piano on a 12.7” iPad Pro, iOS 12.1.1, with a MIDI connection from a Yamaha DGX-505 to a Lightning to USB3 Camera Adaptor, and Lightning to Headphone Jack on the same adaptor. Neither my Beats Solo 3 nor my Sony MDR-V150 headphones will work. If I remove the Camera kit and connect the headphones thru the lightning to 3.5 mm Adaptor cable, both headphones work fine.

When I first plugged in the Camera Adaptor I got an "accessory not supported" message, followed by a query if I wished to update the Camera Adaptor. I assume this was an update to a driver for the USB 3, but I don’t know. I let this run, but apparently it didn’t do anything useful.

Simply Piano does recognize the MIDI connection, so that side is ok.

The last thing I’m going to try is to power off/on the iPad, but I don’t have great hopes.

iPad sold by Apple; Beats headphones sold by Apple; Apple connector kits and adaptors... why does this not work?

John