I recently bought a YYF KUI and I have a problem with the lights.
I noticed that the light in one of the metal cups was flickering and fading faster than the other side. To be a bit more specific, the test I did was throwing the yoyo, stabilizing it with my finger nail, and then looking at the lights: with stable rotation one of the lights seems to have problems. I though it was a battery problem, so today I new ones and changed them. I used a suction cup to remove the plastic cup, in order to avoid scratches. It seems the problem was not the battery and I did not want to work deeper into that in order to not damage it.
Did it ever happen the same to you? Any idea?