To replicate:

Enrol same user in course via different enrolment methods. In this case, I had enrolled the user into the course via a cohort as a student and manually added them as a teacher.

From the Administration block, select 'Course Administration > Users > Permissions > Check Permissions'

The following debug message is displayed on screen:

Did you remember to make the first column something unique in your call to get_records? Duplicate value '5' found in column 'id'.

line 1005 of /lib/dml/mysqli_native_moodle_database.php: call to debugging()
line 121 of /admin/roles/classes/check_users_selector.php: call to mysqli_native_moodle_database->get_records_sql()
line 210 of /user/selector/lib.php: call to core_role_check_users_selector->find_users()
line 171 of /admin/roles/check.php: call to user_selector_base->display()