Setup On a clean site without any cohort created, restore the backup of the course attached to this issue.  It was created using https://sandbox.moodledemo.net/  which is based in master. It has the self-enrolment enrolment method enabled with a cohort in "Only cohort members"). If the following message appears, you can ignore it (it will be displayed at least when testing in 3.7): " This backup file has been created with Moodle 3.8.1 and it's newer than your currently installed Moodle 3.7.4+. This could cause some inconsistencies because backwards compatibility of backup files cannot be guaranteed. " Testing instructions Go to the restored course. Access to the Participants page, click the cog and edit the self-enrolment instance. Check the self-enrolment form is displayed without errors.