My TOC is out of order when I generate to HTML Help. It looks fine when generating to HTML5 output. Have tried re-creating a new HTML Help preset and still same issue.
You haven't said which version you have. I'm guessing it is 2020 as it's a known issue fixed in an update as already covered in another thread.
See the Featured post in the forum to see how to update. You can't update from 2020.0 using Check for Updates.
See www.grainge.org for free Authoring and RoboHelp Information