Pain de Campagne (hybrid sourdough)

Hey everyone! I came across this forum and it seems like a super warm and friendly place to trouble shoot some bread issues. I have been working my way through FWSY and finally finally managed to get a strong sourdough starter and attempted the Pain De Campagne which is sourdough that uses a 1/2 tsp of commercial yeast for an extra boost in rise. 

I followed the recipe through. Everything looked beautiful. Bubbling, bulk fermentation was gorgeous. Shapes, tossed in the fridge after 5 hours on the counter (kitchen low 70s temp), 13 hours in the fridge then right in the oven into a baking cloche I use. Poor bread came out like so. Actually pretty happy with the crumb compared to my previous sourdough attempts. But man that spring was no good. Very frustrated but want to get this right. I will say that I cut the recipe in half. Want to get this down before pouring a bunch of flour into a recipe. 

Did some slap and folds after bringing levain and all ingredients together. I did 4 folds in the first 2 hours right in the bowl. Right after fermentation, for shaping it was a quick quarter fold around the dough, flip, and the pinky pull for tightening. 

The recipe overall is at 78% hydration. I didn't find the dough unmanageable at all. 

What could have been the overall problem here?

Over fermented? Over/Under proofed?

I dont have a thermometer to test the temps of my bread but I've had pretty reliable results before. Should I drop the hydration?