Any chance the hopper is to big? Reason I ask is if hes starting to eat it then stops (20min to me is a long time), its not like he wasnt hungry or unintereted in it to start. Something stopped him.

Other thing is I have had a few times when, for some reason, they have trouble finding the head of the mouse and after a while get frustated and the mouse gets cold and they leave it. Once I reheat it and present it again they hit and normally eat fine.

Good luck