My loaves were on a hot streak during the winter and spring months (I started home baking sourdough late last year) and looked great once I found the right recipe, but my last few have been disappointing, to say the least.

Could it be the fact that my house is now cooler inside as opposed to warmer before (66-68°F compared to >70°F)? Am I suddenly doing something wrong in dough-making or baking process?

This time, I fed my starter a little longer than usual (I typically take it out of the fridge and feed it two-three days once or twice a day and then make the day whichever day I have time), but used the usual recipe (100 g starter, 400 g warm water, 400 g bread flour, 100 g whole wheat flour), rested for 30 min, added salt, then did three stretch and folds over 3 hours, proofed for about 1.5 hours (30 minutes in the oven with no light on by mistake), it looked relatively doubled so I bench rested for 30, shaped, and let rest overnight before baking (~9-10 hours).

I baked it the same way as always, too, 490°F for 25 min covered and then uncovered for 15 in the dutch oven. I always have a cast iron below it with some ice to help steam. I don't know what happened, so any advice would be hugely helpful!

Help! Any ideas why my loaves are suddenly going flat?