I was able to resolve this by doing the following:
Doing an online repair of Office 365 seemed to resolve the 'property does not exist' error.
Still seemed to get the 'We're still setting up this team', however.
Realized that when clicking the channel to try to share, it was always populating from 'recent locations'. If we typed the channel name in full, and it looks it up from fresh, the share was successful.