Had the same issue since saturday morning. It's definitely Google's doing, they changed something that broke Wii U browser.
Deleting cookies won't help. Nor ports āadviceā (you can rely on EA for giving incredibly bad advices like opening ALL you ports for everyone).
I even downloaded and tried Youtube official app, but it also works randomly. At least it doesn't crash...
I guess google people become irritated that Wii U had the superior Youtube experience and decided to ruin watching their videos on Wii U as well, like they did on PC. Do no evil, my ass.