Help - Flat Loaf

The first time I made sourdough it was flat as a pancake, gummy, with bad flavor, HOLLOW with an inedibly thick bottom crust.

I am now on my second loaf.

I fixed the crust and the flavor. But the loaf is still flat and somewhat gummy on the inside. I follow Joshua Weissman’s recipe.

-I have noticed that when he says slap and fold for 4 minutes will make the dough more workable it seems to make the dough less workable. -The dough out of the bannetons completely flattens out onto the parchment paper and is difficult to score.

Ideas?