In Greek Wikipedia we use the user's main sandbox page as a [[ https://meta.wikimedia.org/wiki/Grants:Learning_patterns/Use_an_article_nursery_garden_for_each_new_editor | nursery garden ]] for new articles. More than 200 users have been trained so far to use this functionality and it has been broken suddenly.
As soon as a new subpage was created as a sandbox inside te main sandbox of the user, the new one appeared automatically inside the sub-sandboxes list of the main sandbox. For a week or two now, it appears only half an hour later.
Try it [[ https://en.wikipedia.org/wiki/User:ManosHacker/sandbox | here ]], either by creating a new page or by renaming one. (Well do not move these test sandboxes to an article. If you did, the non existing sandbox would still appear inside the list!)
If main sandbox is edited by source editor and saved, even without changes, the list gets updated and works as usual. Please restore functionality.