The issue occurs because the gadget changes the 'id' attribute on the heading, confusing our code into thinking that it's dealing with Parsoid HTML, which has a different structure.

@Krinkle It looks like you're the maintainer of that gadget. I'd like to propose the following changes to it:

• https://www.mediawiki.org/wiki/Special:ComparePages?page1=MediaWiki%3AGadget-vector-headanchor.js&rev1=4378923&page2=User%3AMatma+Rex%2FMediaWiki%3AGadget-vector-headanchor.js&rev2=4583609
• https://www.mediawiki.org/wiki/Special:ComparePages?page1=MediaWiki%3AGadget-vector-headanchor.css&rev1=4385247&page2=User%3AMatma+Rex%2FMediaWiki%3AGadget-vector-headanchor.css&rev2=4583610

Thanks, I'll test/verify today. There's a lot of subtle bugs to avoid there that I haven't all documented equally well. But looks promising from a quick check. I think you've managed to find the one spot that used to be near-immutable but has been freed/obsoleted by a recent refactor.

https://meta.wikimedia.org/w/index.php?title=Steward_requests/Global_permissions&diff=21554445&oldid=21553946&diffmode=source

Done:

• https://en.wikivoyage.org/w/index.php?title=MediaWiki:Gadget-vector-headanchor.js&diff=4229758&oldid=2461195
• https://en.wikivoyage.org/w/index.php?title=MediaWiki:Gadget-vector-headanchor.css&diff=4229759&oldid=2461194