Quoted from Sohal1025:Nothing stopping it. If there’s not much momentum, the slope up is just too much to get over the highest point before it starts going downward. Does that make sense?
Few potential fixes come to mind.
What's the pitch of your machine? May simple adjustment of leg levelers?
Where the wireform attaches down by the slingshot, is there a thick washer that can be replaced with a thinner one?
Does the wireform dip where the balls are getting hung up? Bend it back up?