"joinable" toggle missing when editing a group

When I tried to edit my group & make it unjoinable, the toggle was missing. This seems to be happening when the group has a sub-group under it. For example, I have an "all members" group, with a free group as a subgroup & then created a few interest groups as subgroups of the free group. If I want to edit the free group to make it unjoinable, that's not an option now. I can't actually even see if I made it joinable or not. The main "all members" group is editable and also the 3rd-level interest groups are editable.