Do you use a stabby thermometer to tell when your bread is done?
This is the best way. Time is not always the same on each loaf, so you stab your thermometer into the center and bake until XXX°. (sorry, been too long, i am into quick breads now)

The outside of your dough gets harder (because it is exposed to the air and heat first) so it can encase the still raising dough inside. Thus, slicing slits, allows the inner dough somewhere to expand.
And you use a very sharp knife (like a razor blade) so you do not squish the raised and delicate dough.

What dough conditioners are you using?

Good job.