Cold fermentation -- flop

 Hi everyone, I

joined the ranks of amateur sourdough bakers a couple years during pandemic lockdown, like so many others. I have found this site so helpful! I have an active starter and have had decent success with weekly bakes. This weekend, I tried the 100% whole wheat for the first time (using Whole Foods _white_ whole wheat). The grain was quite fine, and I did not use a sifter. I had 84% hydration dough, and used a stiff levain. I was very optimistic, as I had transformed an incredibly sticky dough into a tight, smooth and somewhat ball with 3 sets of 10 minute slap-and-folds. I then let it bulk ferment, doing three sets of gentle stretch and folds at 60, 90 and 120 minutes. Unfortunately, I then needed to leave the house for a few hours. I was afraid the bread would over-ferment (dough temp about 77). So, I put the dough in a fridge from 6:30pm to 7:30am the next morning. I then shaped it and let it sit again on the counter for two hours (heating the oven and the cast iron pot in the meanwhile). I baked for 40 minutes at 460 degrees, half with lid on and half with lid off.

In any case, the bread was a total pancake. I am trying to understand what went wrong, as the dough felt really good before I put in the fridge (though not yet fully proofed or bubbly). It did not rise at all in the fridge, nor in the two hours this morning. Might I have overproofed it, by letting it rise in the ambient temperature again this morning (house about 70 degrees)? Or perhaps underproofed?

Thanks for any thoughts you have!