Can't upload files to an Office 365 Group even though I am an owner

A staff person in my 65 person org recently created an Office 365 group.  I wanted to add files to the group, but I wasn't a member of the group.  Since I'm an admin, I added my user name to the Office 365 Group and then, for good measure, I made myself an owner of the group.

I see the group now, but I cannot upload any files to the files area of the group.  There's no option to upload files or drag and drop them.  I can upload files to any other group I created - but I didn't create this one.  

Any suggestions on how to correct this?