I was having the same issue when Fire TV went to sleep with Harmony 650 and Flirc. After trying all suggestions I thought it might be my IR repeater, which it was not. I had an old USB hub and thought I'd used it as an USB extension so it a clear line of sight. It has worked flawlessly ever since!!! I'm not sure if the Fire TV keeps the hub awake all the time and makes the Flirc available when needed. All I know is it solved my problem and thought I would share so others could test it out. Let me know if this works for anyone else.