I'm a bit new to sourdough baking, and freeform baking in general. So bear with my newbie questions!
I've tried a few loaves with the my sourdough starter, both wholemeal and a mix of whole and white flours. The sourdough seems perfectly active and the dough always rises nicely (doubles in size) during the first rise. The trouble starts between the second rise in the proofing basket and putting it into the oven.
When I turn the dough out of the basket, it flattens appreciably, and even more when I slash it. It doesn't rise very much in the oven.