Having hidden sections have a problem on the numbering of the chapters.
The chapter titles show an X for hidden chapters. This is great because it makes chapter number matches with the ones the student will see (so giving instructions will match).
However, on the TOC it shows a normal numbering.
On the screenshot you can check 3.1 chapter on the TOC is shown as 3.X on the title and following that: 3.2 chapter on the TOC will show 3.1 on the chapter title.
I would add the x's to the TOC so numbering will match with the student version.