Steps to reproduce:
- Login as admin.
- Create a course. Enable completion tracking for this course.
- Add an activity to the course (let's say, an assignment).
- Create another activity to the course (for instance, another assignment). During the activity creation, add a restriction with "Activity completion" and select the previous activity.
A label-warning is displayed next to the delete button x (a screenshot is attached to display it).
I've been able to reproduce it only in master (in 3.8 is working as expected).