In the course members management --> groups one can see a column "Coach" and "Assigned". Assigned only shows the number of group participants.
In the course editor when setting the access for a course element depending on group, only the column "Enrolled" is displayed - it shows the assigned group participants. If there is a group with coaches only, but no participants, one might think there are no members in this group at all.
Add the column "Coach" in the group selection mask to provide more information.