Good morning!
After you guys and gals answered my collapse issue, I haven't had a loaf collapse on me since! So thank yall for that... I do have another issue that happens every once in a great while, these hollow spots on the end of the loaf. As you can tell by the picture, the middle is a nice square. This typically only happens when I make my bread Pullman style.
Image
Looks like every now and then you get a big gas bubble tapped inside. I'm a crust fan and like when that happens (that layer of crust is especially tasty). But, try a bit of a punch down before proofing - that'll take care of things. Enjoy!