Hi,
I see a lot of posts along the same lines, but nothing really concrete on what the problem could be. The Playgrounds app running on my Samsung SM-T800 doesn't recognize my keyboard. I am running Android 6.0.1. The USB Midi monitor on the Play Store recognizes the keyboard fine, and shows what keys I am pressing. The Playground app doesn't seem to recognize the keyboard at all.
The keyboard enumerates as Class: Audio Device (0x1). There are no endpoints on Interface 0, and there are 2 unidirectional bulk endpoints on Interface #1 - one in and one out.
I can give more information if you guys want to debug.
Jerry