I made a chocolate cake and recipe calls for buttermilk and oil which makes the batter liquidy,but when I bake it, they turn out rubbery or they become very dense and when I press it feels like soft boiled chocolate paste like texture and also they crack on top, it only happens with the runny batter recipes and thick batter recipe cakes are perfect and super fluffy,what could be the problem?
I bake a lot with gluten free (I cater for a wheat allergy) and as a direct result a lot of my batters are runny but I still get a fluffy final cake. Bread doughs are more like batter than bread too.
You mention folding in the comments, which prompts me to wonder if you're making a red velvet cake, given the recipe points mentioned.
If that is the case, you need to aerate the egg whites separately, and fold them in last, taking care as to not lose the air you put in.
If you edit your post to include the recipe that would help with diagnosis a lot more.