I have very much been enjoying the app! One odd thing is that previously, like within the last week, I was able to use the USB keyboard that came with my tablet to play ROMs. I mapped through the settings as appropriate and everything was working great. Then out of nowhere, the keys wouldn't work. No amount of tweaking settings or clearing data would help; even completely reinstalling the app failed. The device I use is quite large and holding it for a long period of time to use the virtual controller is a lesson in endurance to say the least.
I did some testing myself and finally determined that the key mapping function in the settings is only remembering the last key entered. Like if I map the left key, right key, up key, and down key to their respective d-pad locations in that order, only the down key will function in-game.
Not sure if there is an easy fix like a setting I am missing, but I have been over every screen and tried just about everything I can think of to deal with it. Nothing has worked. Hopefully someone here can help!