If you did not lube the inside of the necks,it will pull the shoulder back up,as you pull the sizer ball up thru!!!!
Just what i have found,over the years,with the dirt in the necks of fired cases.To brush them and dry lube ,is a big help,with this problem,if it isn't the die!
I would venture to bet that it isn't all of the cases,doing this,is it????
KEEP TRYING,you will figure it out!!!!!