When you go to Manage Custom Groups, some or all students are greyed out in the list of students in an existing custom group. You may see a tooltip message reading "Student has become unrostered or is otherwise unavailable".
Students who are assigned a custom group but who are not rostered to the current term are listed in grey text.
The student is still a member of the custom group. If the custom group was created in the current academic year, they should still appear in MAP Skills under the custom group heading. However, until they are rostered for the current term, they will appear in grey text. See Unable to add students to a custom group for more information.