I'm not sure whether you're using Tiramisu or Aroma (or something else?) but if updates are blocked in any way, such as the update folder being deleted or trying to update while running in Tiramisu, it's always just going to say it's up to date. You'll need to recreate the update folder if it was deleted and boot into the standard firmware. Make sure you don't have a disc in the Wii U either, that can cause other issues.