Track changes and editing the table of contents

[hhhava]

Hi I am editing a document with an existing automatic table of contents (someone else authored this document, and I'm supposed to update it), and I am editing with track changes on.
To be clear, here is what happens.
Example document

Table of contents
1Introduction
1.1 Welcome
1.2 How are you?
2 what to do
3 conclusion

Document
1 Introduction


1.1 welcome to blah;lakjd f;alksd fa
1.2 We hope you have had a nice journey. How was it?

2 what to do
las;sdjkfa ;sd
3 conclusion
af;lsdkjs ;


I go in to add a new section after section 1.1 I select the same heading for the new section as the other sub sections have. But find that numbering isn't turned on. So when I hit enter to make what will now be new section 1.2, no number 1.2 appears and what's worse, the old number 1.2 doesn't automatically become 1.3! But the new title will automatically populate in the table of contents, but not the number?
Did the person who made this document actually mannually number the sections? I can't believe this would be the case. Then I'd have to manually change all the following sections! crazy. Or am I missing something? Is track changes incompatible with updating the TOC? Should the numbering possibly be assumed feature of a heading format? If so, why isn't that working? And If not, how can I fix it, and retain the style of numbering Heading 1 with the whole numbers, Heading 2 with the decimal sections?

Thanks!