I noticed T205054 and we have the same issue on donatewiki. On pages with a table of contents in the side bar, it's possible to jump to any section and get there via a smooth-scroll effect. However, this effect seems to be breaking the normal handling of fragment links by not actually changing the URL in the address bar.

Will need to change the smooth scroll code in https://donate.wikimedia.org/wiki/MediaWiki:SupportPage.js