HELP: Chapter 2 is followed by Section 2.8, instead of 2.1

I don’t remember I have changed compile settings. But when I compiled the binder recently, I just noticed that the section, which previously was printed as Section 2.1, now is Section 2.8.

It’s 2.8 because the last section in chapter 1 is 1.7. Where have I missed? Thanks for helping me out!