Creative Cloud Files not syncing between computers in adobe premiere team project

Hi Sarah,

I assume when you mention 'shared creative cloud library' you mean a shared 'Creative Cloud Files' folder, or are you in fact refering to a shared Library in Premiere Pros Library panel?
Have you confirmed that your CC Files folder are fully synched, so both of you have the exact same files locally on your respective machines? 
Can you create a Media Mapping for the offline files?

• Edit > Team Project > Media Management
• Select the Offline clip or its parent folder
• Click the 'New Media Mapping' button and point to the location or its parent folder where the offline clip(s) are stored on your machine.

A common culprit for media to appear offline is when one of the collaborators used (File > Link Media...). 
Important: In context of a Team Project you should almost never use the 'Link Media...' option.

Best,
Udo

Who is the project 'owner' and who the invited collaborator?

The owner can add media via the Project panel and share changes, but all collaborators must add media in the Team Projects Media Management dialog ... as if you don't, when someone else adds media to the project via the Project panel, it changes the reference for all others.

Yea, I did that. And I'm wondering if that is what is happening for you, because that is what I did to my partner, who was the original creator and 'owner' of the project therefore.

Neil