Ability to Share Collections in Content Hub

Hello, 

I have a user who seems to have all-but-Admin rights to AEM Assets, and has access to Content Hub. He is however unable to share Collections. When he creates a Collection, the only option for who has access is “Only you and admins can view and edit”. 

He says he has previously been able to create a collection and give public access, but this was only to one Collection. We’ve not been using Content Hub for too long so not sure what I might be missing!

Thank you

Lana