Lazyscience
Bluelighter
either the substances you take are different chemicals or your expectations of the effect is different which could affect your subjective experience. different doses would also cause different effects too. there are a lot of factors that could affect the way the mdma affects you like set and setting. i think its most likely that they are cut with different chemicals and thats why you get different effects or that they contain maybe no mdma and have mda instead or some other drug. who knows?