These loaves didn’t keep their shape when shaping, but turned out great?

Both loaves followed the below recipe. Loaf on left in first pic is the first crumb pic, loaf on right in first pic is the second crumb pic.

I made these loaves together and only split them when pre-shaping. Neither held their shape well during pre-shaping, and both went kind of flat when I turned them out for scoring. However, crumb came out great, so I don’t think it was a proofing issue. I left my leaven out much longer than the recipe called for (probably 12hrs+ vs the 6 hrs called for), because my kitchen was cool and I forgot about it. Could the shaping issue be from weak starter?

Other things to note: I used a proofing heat mat for the first time with these loafs. The mat heats to and stays at 80F degrees. Lastly, the crust came out soft, and I’m not sure why. Thoughts?

Ingredients:
For the Leaven:
30g 100% hydration starter
65g water
65g bread flour

For the Dough:
620g water
605g bread flour
200g whole wheat flour
16g sea salt
160g leaven

Process:
Build leaven 6hrs before making the dough. Make slurry with starter and water, add the flour and stir to combine. Cover and allow to ferment at room temp until bubbly.

Combine the waters and flours. Cover with plastic and allow to autolyze for 1-2hrs. Sprinkle salt over dough and mix with leaven until completely incorporated. Cover with plastic and allow to autolyze for 20mins. Remove dough from bowl and perform slap-and-fold method for 5-6mins. Cover and allow to bulk proof for 3hrs, turning and folding every 30-45mins.

When dough is puffy and almost double in size, divide in half and preshape. Cover with plastic and bench rest for 10-30mins. Final shape and place seam-side up in floured banneton or couche. Cover with towel and then plastic and refrigerate for 8-24hrs.

Preheat oven to 500F with Dutch oven inside. Remove loaves from fridge and allow to come to room temperature for at least 1hr. Score loaves. Place loaf in Dutch oven, close lid, and return to oven. Lower heat to 470F and bake for 20mins. Remove Dutch oven lid, and bake for another 12-20mins.