did you follow gen3sf usbloading guide for that? (questions on that could go there)
and made the wbfs partition primary?
i like Fat32 loading (linked below) as i can have games and apps on the same drive without partioning, recongnized by almost all loaders, i use wiiflow and cfg usbloader.
do you still run wiiflow from sd card or from that newly created exFat part?