I am having the same issue as admin and creator of my group.
"To do that we require a more intentional sharing workflow that is done from the item owner’s content page" is irrelevant for the issue raised since the problem occurs even for item owners.
Why isn't the admin and owner the material not able to see a group under access and update but able to see it through access? And yes when it was created members were given the ability to add content. Very odd.