Recently Canvas added a new feature option to profile settings, that does let you choose how columns are seperated in the gradebook exports.
There are other places where a user can make csv exports (f.e. quizzes) that are not affected by this setting. This means that users will sometimes get csv's with semicolumns and sometimes get csv's with comma's.
Idea: Change the feature option to Use semicolons to separate fieldsin csv Exports, and us it for all csv exports.