Screenshot of warning message: "Illustrator now honors 9-slice scaling of symbols. Any scaling done on symbol instances with 9-slice scaling option in legacy version will look different now. Do you want to retain the 9-slice scaling option for symbols?" Options are Yes and No, with a "Don't Show Again" checkbox.
https://xoxo-media.sfo2.cdn.digitaloceanspaces.com/media_attachments/files/112/333/444/008/321/797/original/7f27dd46c30ad9c3.png