Gummy/ tacky looking holes

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Hello,

  I tried my hand at my first sourdough this week using Ken Forkish's overnight blonde recipe. For my first attempt I followed the recipe exactly and figured that I had at least three hours of proofing time so I went for what was supposed to be a quick grocery outing. I got back and the dough was over proofed and the more I tried to fix it the worse it became. After reading posts on this forum regarding that recipe I gave it another try, this time relying on sight and touch to determine when I bulk fermentation as well as final proof were done. I baked the loaf and it looked really good until I cut into it. In some of the holes it looks under cooked or tacky/gummy maybe? I'd like to ask what may have caused this. Thanks in advance.