A few weeks back, out of the blue, I had the exact same thing happen. What I did was disconnect the box and pull the power. Gave it 5 minutes or so, reconnected, and perfect again ever since. I am not technical, but wondered if just a surge..or drop maybe..of power and/or signal could be the cause ?
Not mentioned if you've tried this already - but worth a shot if you haven't. Could be just that simple..hopefully.