Sourdough crumb is spongy

Hello,

i started making sourdough bread only 2 months ago and have struggled to correct this issue. The bread comes out beautifully and tastes awesome but is a bit spongy. I am following "the perfect loaf" blogs beginner sourdough recipe shown in the picture. I have a strong starter that I am using and everything feels and looks right throughout the process. I perform 3 series of stretch folds 30 min apart then let rest for a total of 4 hrs. It then gets shaped and another short rest before getting placed into the lined bowl and covered for retarding in the fridge for ~16 hrs. The Dutch oven is preheated to 500F for an hour and the dough is taken out of the fridge and left to rest during preheating for 30 minutes. Baked on a parchment sheet covered at 475F for 40 min of one loaf or 20 if halved into 2 smaller then uncovered for 40 if single or 20 if halved @450F. Temp is checked and has always been 212F but a bit sticks to the temp probe. 

Ideas?? Thanks for the help!