I notice that completed mastery goals are not removed and still continue to show the keep learning button.

It might be nice if they would complete in some way.

Perhaps show a message completed (and date maybe) with the keep learning smaller and to the side as link or removed altogether.

Students should be able to remove completed mastery goals from their dashboard.

Completed mastery goals being then listed separately on the assignments dashboard under a little tab like past assignments are currently displayed.