Whenever I try overnight fermentation for better flavor, I find that bread won't rise so much after it has been shaped. The dough rises beautifully during the first fermentation on the first day so yeasts were definitely active the night before. Is it possible that yeast has died off overnight? I follow the rather conventional procedure of kneading-first fermentation at warm temperature-deflating a bit and putting in fridge overnight-shaping-proofing-baking. I allow adequate spacing during proofing process and of course overnight fermentation is done in the fridge.
Overnight proofing in the fridge is a great way to improve flavor, as you suggest (creating more alcohol and allowing a better gluten structure). There are a couple of things you should keep in mind. First is the temperature and length of your bulk fermentation. Too long and/or at too high a temp it could be using up most of the sugars, and the yeast could be simply running out of food. Are you doing this fermentation above 75°F? Second, too much salt in the dough will negatively affect your proof.