Well, my brother Michael had a major problem suspending his disbelief for something that happened in chapter 27, and after discussing it with him, I decided he was right. Fortunately, I was able to come up with a satisfactory alternative, but I had to make some major revisions to chapters 27 and 28.
There are several parts I’ve already written that I know I will have to go back and revise later. (For example, chapter 21 has a real As-you-know-Bob problem with the dialogue.) But those required revisions are mostly about style and clarity. This one was important enough a change that I didn’t feel I could proceed further until I had fixed it.