I use Apple TV (4th Gen) as my main source for TV.  You're right it sounds like it's been unpaired....But you don't "need" to pair the apple TV to get it to work with the URC  IR codes.

That being said...I've been having a similar issue with my 4th Gen. It's not in a closet, I can see it from the couch.   When I press the button, the white light flashes, but no love. (I'm using the apple TV remote).

The fix for me is to unplug and plug back in. To give you an idea, I've had to do this 4-6 times in the last month or two.

I've also been experiencing a problem where the specific app..will open, but it's just go grey screen.