The post-edit dialog (T245790: Newcomer tasks: post-edit dialog) should be displayed right after saving the page, which MediaWiki notifies about via the postEdit / postEditMobile hook. Right after the event is being triggered though, the page might get reloaded. The post-edit dialog tries to account for this, by setting a sessionStorage flag and re-displaying on the next page, but this might fail when the time between the hook call and the reload is long enough that the reload detection code thinks it is safe to remove the flag.

Specifically, this happens when saving via VisualEditor, and either the page did not exist before, or it was started in the source editor. Neither of those cases are covered by guidance so this is not an immediate problem, but should be solved eventually.