I bought a new Wii U a few months ago. I most often play Mario Kart Wii (in Wii mode) and have been noticing an increasing amount of fits of controller lag.
I know that the Wii isn't known for lagless controllers, but this isn't typical .1 or .2 second lag for all input. We'll be playing fine for twenty minutes, then all of a sudden the Wii will have one of these "fits" where all controller input lags and becomes extremely choppy. Pausing the game and waving the Wiimote slowly in front of the TV reveals that the Wii is picking up inputs only 3 or 4 times a second. (i.e., the hand icon stands still and jumps back and forth: choppy.)
Resyncing/resetting the Wii U stops the problem, as does waiting it out sometimes, but it makes many games completely unplayable when you suddenly lose control. What can I do to fix this broken Wii U?