I ran into a weird issue on the Wii U's Warawara Plaza a few days ago, and it still has yet to clear up. After weeks of it working without a hitch, I left town for a few days and when i came back, the plaza no longer updates. It doesn't display friends' Miis, all of the messages that pop up are generic Nintendo messages, the plaza isn't displaying games anyone is playing (just icons for things like Miiverse, the eShop, video chat, and so on), my Mii keeps telling me that I'm playing Scribblenauts Unlimited (I've been playing Ninja Gaiden 3 for the past several days), and it doesn't update to display new information. The Miiverse is unaffected, as far as I can tell.
What's more bizarre is that I called up Nintendo's support line, and they were completely baffled by the issue; it was forwarded to a supervisor who's supposed to get back to me in a day or two. But I actually just checked Google and found that others have been having the issue dating back to at least early December. There doesn't appear to be any clear way to resolve the issue.
Just thought I'd post this warning in case anyone else sees this happen on their own console.