1. Create a course in visible group mode
2. Create a couple of groups
3. Enrol a student and add them to one of the groups
4. Login as this student
5. Go to the course participants page
6. In Moodle 3.8 - you will see your group by default
7. In Moodle 3.9 - you will see all participants without groups filter by default

I don't know if this is intentional, just bringing your attention to it. It failed one of our behat tests but we can fix the test easily to expect different default