For each team we create we add a library in the teams sharepoint site and then add a tab in teams with a link to that library. The idea is to have your work in progress in the teams files library and when you have finalized the document you move it to its permanent location in the library we created. I tested this in the past and there was no problem moving files between the libraries. However a user had a problem moving a file last week and it appears MS has changed something? Now we can only move or copy files between the 'standard' files libraries that teams creates. All the libraries we created in sharepoint are no longer visible within teams. If you open the 'files' library in sharepoint you can still move files but that is an extra step and we would have to retrain users. Is this by design???