Docs affix subitem not highlighted on master

[XhmikosR]

I think I've seen this issue again and it was fixed, if anyone finds it let me know.

[carasmo]

Works fine:

What browser and version?

[XhmikosR]

Doesn't matter, it's not a browser issue. Happens with all the browsers on master docs, not on the website.

[juthilo]

X-Ref: #13659

[juthilo]

Doesn't seem to be broken all the time, i.e. sometimes it doesn't work for the first section, sometimes it doesn't work for any sections and sometimes it works fine for all sections.

My testing suggests it works if I scroll down before the page finishes loading.

[juthilo]

Scrolling down before the page is ready only makes the first section on that page work though.

[juthilo]

Ok, I tried reverting d15444d because not much else changed in scrollspy.js and it does indeed seem to be the culprit.

Is there any other way to fix #13071?

/cc @hnrch02