Can Not Add Team Member

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I am using the free version of MS Teams. For one individual, I attempt to add them at the TEAM level, but without success. 

iPadOS App: If I attempt to add them, they appear in the list of members, but I get an error if I try to make them an owner. I also can not force remove them, but after some period of time they will be automatically removed. While they are listed, I try to add them to a private channel, but am told a member already exists.

Web: Using the web interface, I attempt to add the user at the Team level, but nothing happens. The name doesn't even appear in the list of members. No reported error in the user interface.