So I’ve been trying to recreate the German sourdough rye of my childhood. I’ve got the flavor profile down but when I bake the loaf looks like a thermonuclear mushroom cloud. Recipe is 1 part dark rye sour to 4 parts AP wheat flour with a tablespoon of oil and molasses and a 1/2 teaspoon of salt. 1 packet dry yeast. No added water unless the dough is too dry. (Sour is the consistency of pancake batter). Bake at 400 DEG F for 40 minutes.
I’m kneading the dough for 15 minutes by hand and get a nice soft dough. I proof for an hour (70 DEG F) covered and then punch down and form the boule. This goes on a baking sheet with some flour and I invert a large bowl over everything to keep moist and allow to rise for an hour.
The photo didn't make it. But from your description, you may have had a "blowout".
That can happen if you are baking an uncovered loaf in a convection oven.
If you can't turn off the fan, you'll need to cover the loaf somehow. Perhaps use a dutch oven, a cloche, or an upside down steel bowl.