Is my starter to blame?

Hi all. Probably loaf 10 or so, not really sure what I need to change.

Left loaf was in a bread pan and right loaf was in a Dutch oven.

Both loaves

100G starter (wouldn’t rise past about 1/4-1/2 of its initial size)

500g KA APC 350G warm water 10.5G sea salt

Mixed together in two separate batches with a stand mixer for about 5 minutes

30 min interval stretch and folds 4 times

BF for about 6 hours in my oven with the light on, bubbly and bubbles, pulled away from bowl edge nicely.

Shaped the DO loaf into a banneton and shaped the bread pan and put in bread pan.

Cold ferment for 12 hours.

Baked DO loaf at 450 30 min lid on 15 lid off to 207 internal

Baked bread loaf 450 30 min with water in a pan, about 20 min out of the pan directly on the rack.

Cut 8 hours later

Hi all. Probably loaf 10 or so, not really sure what I need to change.

Left loaf was in a bread pan and right loaf was in a Dutch oven.

Both loaves

100G starter (wouldn’t rise past about 1/4-1/2 of its initial size)

500g KA APC 350G warm water 10.5G sea salt

Mixed together in two separate batches with a stand mixer for about 5 minutes

30 min interval stretch and folds 4 times

BF for about 6 hours in my oven with the light on, bubbly and bubbles, pulled away from bowl edge nicely.

Shaped the DO loaf into a banneton and shaped the bread pan and put in bread pan.

Cold ferment for 12 hours.

Baked DO loaf at 450 30 min lid on 15 lid off to 207 internal

Baked bread loaf 450 30 min with water in a pan, about 20 min out of the pan directly on the rack.

Cut 8 hours later