@VirginieJouffre Welcome! In addition to @J_Kurosaki's suggestion, another reason why your courses may have disappeared is if there was some kind of change in your student information system. Sometimes, when data changes in the student information system (such as correcting terms, course code, changing 'primary' instructor, etc) that may trigger Canvas, on the next sync from your student information system, to make a brand new course, which may look like your course got deleted/removed. If this is the case you'll want to contact your institution's Canvas support to investigate if this has happened.