Hello.
That could be
maybe a HDD Intialization/Re-Intialization Issue.
- How is your vWii´s cIOs Setup (249 and 250) please ?
- How is your HDD connected please ?
(Y-USB Cable or Single USB,the Wii U needs "more" Power for the USB HDD´s because of the different (USB)Architecture fro the Wii).
- Do you have an Additional Power Supply for the HDD ?
- Which USB Ports on the Wii U did you use (maybe your HDD works better on the back Ports if you did not already tried it).
- Which Version from the USBLoader GX did you use please ?
Of Course you can try the other USBLoaders Wii'Flow/WiiFLow Lite MOD/Configurable USB Loader.If you have the Same Issues,then maybe one of the Points above could help you.
Thank you.