Creative Cloud: File not syncing to view-only collaborator.

I am sharing some design files with collaborators that don't need edit rights. Therefore I am sharing the folder with them as view-only. One of the files in the folder stopped syncing (all the rest work fine) throwing up the following message: 

"<File name> cannot be synced because it is in a view-only collaboration. You cannot modify, rename, or create files in a view-only collaboration. To sync this file, move it to a read-write location within your Creative Cloud files folder."

This makes no sense to me. A core part of the functionality of CC is that some folders can be view-only. Why would this message come up? How can we clear it and get the file to sync with our collaborators again? We cannot start moving the file around because the file structure needs to remain as is.

Many thanks