@Fulcaire
Found a solution for people having a Problem after installing a game update:
If you have a HDD or USB stick in your WiiU nake sure to move your game specific save file to the internal WiiU "harddrive."
Then use wupinstller to installiert your game update.
Then it works.
The Problem is, wupinstaller installs to the intern wiiu "harddrive". When you have a USB stick or HDD in your wiiu the game will choose this and cant update.
After its succesfull, you can move your update and save files to the USB stick.
I had the same Problem, as i only have the Wii u basic and a 32gb USB stick
I hope you guys could unterstand what i mean. Since english isnt my native tongue