Thanks !
I wanted to answer sooner but couldn't : Yes, it was USB related.
Here is the whole story :
I bought a second hand Wii U to play to Zelda: Breath of the Wild and didn't want to buy a Switch the full price.
I have an old Toshiba hard drive 320GB. This drive have two holes, one for the mini USB plug, the other, 3mm circular jack hole. The original package provided a USB jack plug.
On my original, hacked, Wii, I didn't have to use this cable. Single USB plug was working perfectly. I removed partitions so my Wii U could handle it as a brand new drive.
I realized the Wii U couldn't recognize my drive so I connected the "USB jack" to the second Wii U USB port and everything worked perfectly. Notice I didn't hack vWii.
1) Why I have no problem with my original Wii and need a USB Jack on the Wii U ?
Then I wanted to play GameCube Mario Kart: Double Dash and install vWii HomeBrew Channel + Nintendont + Wii U Nintendont forwarder. I put the Mario Kart iso on my SD. Everything worked fine.
2) Why ? Nintendon't is the only hombrew that work perfectly.
Then I tried to run USBLoaderGX, snes9x, smw, save manager gx then realized none of them works.
I unplugged USB hard drive, and vWii homebrew works perfectly. I tried to swap the USB plugs so power USB was on port one and it work fine.
So problem was technically solved.
But, now I read you advise to don't use USB with vWii. What do you advise ? It take a lot of space for all games.
Thanks again for your answer !
Edit: As a new member, I can't post URLs.