(Tested with a Moodle 3.2.3 Backend)
The activity completion ticks are not shown for you in Moodle Mobile when you have just the Teacher role in a course and not Student as well.
- To test, set up a course with activity completion activities (manual ticks) and enrol yourself as 'Teacher' only.
- In Moodle Mobile, access the course and tick the activity completion checkboxes; they do not fill with a check tick.
- In this course, add the 'Student' role, other than the 'Teacher' role to yourself.
- Reload the course in Moodle Mobile; you'll see the filled activity completion ticks in the checkboxes