Last night I was trying to get RetroArch and some other homebrew back on my Wii U after not messing with it for a couple years. I could get Nintendont and Not64 working just fine, but RetroArch with newer versions would kick back to the homebrew channel after I attempted to load, and older versions would black screen my Wii U forcing me to power cycle.
I troubleshot the issue down to having the wireless receiver for the Guitar Hero world tour plugged in. My guess is after executing RetroArch, it would scan the USB drives, and when it saw the wireless receiver it would freak out. The other homebrew apps I listed don’t have this issue. Removing the receiver lets RetroArch works and I have no problem doing that, but since its exclusive to RetroArch I assume it has something to do with the way it was written so thats why I brought it up.
Cheers!