Unfortunately i’m not the best with mechanics either so I can’t really help you with that department. I know there is a ‘lemon law’ in california that helps protect consumers against this sort of thing. I think the requirements are the vehicles being in the shop a certain amount of weeks within the first 18 months of purchase.
Your state might also have something like this. Maybe also try contacting a UM rep to see if they know what the problem could be. If it is under warrenty then I hope they will help you without too many problems.
It really sounds like an electrical problem to me. When you first brought it in did they only replace the starter, or did they replace the batery too?
~Best Beginner Motorcycles Admin