After digging into it, I believe I've found the probable cause, but sadly I can't fix or suggest a workaround.
When changing the sort order in the answers or questions tabs of the profile (which works fine), there's an AJAX request sent to https://meta.stackexchange.com/ajax/users/tab
, followed by the user id, and giving which tab and what is the desired sort. E.g., the full URL would be https://meta.stackexchange.com/ajax/users/tab/152859?tab=answers&sort=activity
. (There isn't any point in going there; first change the user id to be yours.)
So, what happens when trying to do it for Saves? This is the URL being requested: https://meta.stackexchange.com/ajax/users/tab/152859?sort=Activity
. As you might notice, the "tab" parameter is missing, so the code behind doesn't know what data to pull, hence throwing 404 Not Found error.
I did try to manually add tab=Saves
, tab=Bookmarks
, and tab=Favorites
but none works. It appears to require a change in the code-behind itself to support the rather-new Saves.