Users are experiencing issues with Custom Header Links in Discourse, where clicking on a link causes a full page reload instead of a smooth transition. jack2 reported this issue and observed that the <a> tags in their production instance have a data-auto-route="true" attribute, which is not present in their development instance. A possible solution was proposed by syl through a forked plugin, but Stephen advised against using a forked plugin. The issue has since been fixed in the official component as reported by Johani, and internal links will no longer cause a full page reload.
Reverting the change from @j.jaffeux breaks internal links in a different way. I wouldn’t use a forked plugin - it just means when this gets fixed for real you won’t receive the changes automatically.