Noise stops abruptly with semi-UI freeze on Amazon Fire 10

[Dan]

After a few hours of play on a custom white noise config with the tablet in standby mode, the sliders all minimize, the preset reads "default", and the noise stops. I then can't interact with the UI except to go back to the main screen and then the UI is usable again. This happens regardless of whether it's in slider mode or at the menu list. Does not happen at the time of standby but some hours later.