It might have been that you overproofed the dough. You have some enzymes working in there that can weaken the dough with time. I usually have a 2 hours bulk proof where I stretch and fold the dough after 20 40 and 60 minutes, and then 1-2 hours after shaping - after shaping I leave the loaves in banettons. Sometimes I replace it with 6-8 hours in a fridge.

But still a nice bread.

BTW: We have a community for breadbakers