Sourdough bread crumb ripped in two
How much steam are you using? You might try baking the first 20 minutes in a french oven* (aka enameled dutch oven) and then take off the lid, but don't add extra steam. If you don't have a lame, use a razor blade or a really sharp boning knife (or a sharp paring knife can also do). 

This kind of problem can also be caused by underproofing, but it sounds like you're doing a good job there. Just make sure the bread doesn't spend too long proofing between your last fold and the fridge. 

Also, just based on the shape it looks like your dough maybe over-hydrated. 

*pre-heat the french oven and lid, though some people omit this step, drop in your bread, cover, bake for 20 minutes, then uncover and bake for 25-30 minutes longer.