My sourdough splits at final proofing (pic included), advice?
There are three likely causes: over-proofing, insufficient gluten development, and too loose shaping. Some combination is probably most likely. To detect over-proofing try the `poke-test': if the dough springs back immediately, the dough is under-proofed; if the indent stays as it is, the dough is over-proofed.

I've found Dan Lepard's advice in The Handmade Loaf for shaping high-hydration sourdough loafs very useful. After final stretches-and-folds, spread the dough into a circle, and make eight folds into the centre, pressing down on the join. Use the scraper to invert the dough and rotate it gently on the work-top for a minute or so. This tightens it up. Then invert it again as it goes into the banneton.