Wow, you are right! It appears that you have found a bug! I was able to replicate it and I figured out the problem. InDesign TOCs, for whatever crazy reason, have a problem pulling in paragraphs containing with text variables. In This case, the paragraph style you reference in your TOC has two different text variables in it: this chapter number, and the Title.
I tried changing the text variable type to a character style running header or a filename,e but the problem persisted. I was able to get those extra page numbers to go away by converting one of those variable to live text, so there is only one variable in that paragraph. The easiest way would be to convert the chapter numbers on that line to live text. That way, you Chapter name variable will still stay live.
Again, as to why this happens only on chapter 10 and up, I have no idea. It’s a very weird bug, indeed. It apparently has something to do with the multiple text variables. I tried having three variables in a paragraph referenced by a TOC, and InDesign started omitting/changing some of the text from the TOC, and pulling in the chapter number of the TOC as a live variable. I changed the chapter numbering style of the TOC so you can see that the TOC is referring the TOC chapter number, and not the actual text from the document. Crazy stuff, I tell ya!
https://4.bp.blogspot.com/-zvvwIty0he0/VY2sP_daAFI/AAAAAAAACOQ/oAVXmufmRIw/s1600/CRAZYTOC.png
Just for kicks, I made that line have 8 different variables, then duplicated the text variable and converted all the variable in that second frame to live text. Then I updated the TOC again. And insanity ensued! Not only did InDesign mess up most of the variables, it also added that extra page number six times! I colored the different text variable so you can see a bit better how crazy this is.
Wha-What?
https://1.bp.blogspot.com/-CiIt1x975Ds/VY2vzicYG6I/AAAAAAAACOc/0HY6EkYujJw/s1600/CraziestTOCEver.png
I would submit this to the InDesign team as a bug: https://www.adobe.com/cfusion/mmform/index.cfm?name=wishform
So again, the easy fix: make your chapter numbers live text in the “Chap Num + Name” paragraph. That should fix it.
*Shakes head in disbelief…