They should still be working as ever. You may have changed the zoom level or possibly we changed some dimension slightly and your screen is no longer wide enoug

They should still be working as ever. You may have changed the zoom level or possibly we changed some dimension slightly and your screen is no longer wide enough to provide adequate space for sidenotes. (And I'd point out that even when you don't have sidenotes, the footnotes are still better than usual because they pop up on hover - no click necessary unless you disabled JS entirely, at which point /shrug, you've indicated you don't want fancy frills so enjoy your old-fashioned 1995-style footnote hyperlinks.)