I don't know what's going on, but for the past couple of days if I try to watch a youtube video via the web browser, if an ad precedes the video the Wii U hardlocks. I googled and apparently this is happening to multiple people. It's very annoying.
Google turned up this reddit: https://pay.reddit.com/r/wiiu/comments/1lvnfm/youtube_ad_crashes_my_wii_u/
Google turned up this reddit: https://pay.reddit.com/r/wiiu/comments/1lvnfm/youtube_ad_crashes_my_wii_u/