Dnk had a few good questions, but I have a few more. The more info we have, the better we might be able to help you with your problem.

Do all of your breadhead shots hit in the same location or do they vary in impact points. Did you check for wobbles in the broadhead (is it alined, tip of point on center axis of arrow).

IT could be the spine of the arrow being too stiff, but with crossbows, it is not usually a problem. One problem I had seen was with a thunderhead (also with two other heads) but only happened on windy days. The heads actually planed with the wind, but they did not hit same point of impact. If the tip of the head does not line up on the center axis of the arrow, it will also wonder, also will not usually hit the same point of impact either.

Hope this helps a little.