I'm using the current Fire TV 4k beta client with the current server beta as of 1/31/2020. There is a consistently occurring bug that occurs when resuming from a pause. When play is pressed, the audio resumes, but the video will either freeze, or will appear dark and missing green. If the back button is pressed, the screen brightness changes as if displaying a dialog,and if back is press again, the video returns to normal. When this occurs, the back button will not exit the current activity. At that point it's necessary to force stop the app.