Owner 3 pairs of sk8 his and never had any issue breaking em in. But recently got a new pair and for some reason, they rub on the heel so much that despite wearing socks, literally end up bleeding after going for a walk. I’ve heard of slips ons, old skools, etc rubbing there. But never boots?
Try “locking your foot in.” I always have my customers literally drag their foot all the way back BEGIRE laving up. Then, you have to tighten from the bottom up. It’s the only thing that secures the foot and prevents rubbing.
There could be other factors in play, but this base method generates a lot of great results.
Good luck!