going off regular hopper tech, i'll try to answer.
i don't know the eye setup in the JRNY, or how it senses it need to feed, but the eyes(which i will assume it has) might not see the paint, or the ball stack is falling in between the eyes, causing the double feeds.
also, check the detents. eggys aren't a force feed hopper, so the ball detents could be fine. but if i understand the JRNY, it has more force behind it, and could be blowing past the detents.
hope that helps.