I want to restrict access to a site in Sharepoint Online.
I have disabled inheritance and created a new Contributor Sharepoint group, called [Site] Members.
When I add Active Directory (AD) group A to this Sharepoint group, and use "Check permissions" it shows the expected result. But when I add AD group B, "Check permissions" shows that its members don't have access.
Both AD groups A and B are non-nested, meaning they only contain users, not other AD groups. They are also both Security groups and similar in every way.
If I add users from group B to the Sharepoint group directly, then "Check permissions" reports that they have access.
Why doesn't group B work?