That sounds like the epub has an error in the .ncx file, and that's because Moon+ uses that exact file to organize the chapters in the reader.
You should check the .ncx in your .epub (you can do that with any text editor app like notepad++ or your windows Notepad, or use Calibre).
Check that Chapter 2 leads to chapter2.xhtml and chapter 3 leads to chapter3.xhtml.
The problem should be chapter 3 from what I read from your post, it may be leading to chapter2.xhtml in your .epub
Edit: Also check toc.xhtml the same way, just in case.