Symptoms
Can not add custom attributes to the "Accountmanagement" >> "ADGroups" Service instance.
They do not appear in the properties dropdown after adding them
Diagnoses
The attributes that are added might not be compatible with AD. Or so we thought.
Resolution
Labs have confirmed that this is a feature request since this is not possible standard out of the box.
Our Dev teams are also working on a custom service broker to resolve this issue.