Group Chat: Make it possible for new participants to see previously shared files
New participants to a group chat can't see files, via the Files tab, that were shared before they joined the chat. This is true even if you give them file access via OneDrive/SharePoint.
Workaround: Remove all files and share them again (ouch).
This seemed like a clear bug, but after consideration, I believe the behavior is intentional and a solution complicated/controversial.
Since a shared file (files are shared in a group chat, not uploaded) is still owned by the person who shared it, if Teams automatically gave access to new participants, then Person A could share a file, Person B could add Person C and Person B would then be modifying access of Person A's file; that would clearly be wrong and is fortunately prevented by current security.
Proposed solution for Files tab:
o Files tab has button "Request file access", enabled when there are files in the group chat for which I do not have access (the missing files are not shown still). Clicking that button sends a request to each owner of a file, for which I do not have access, requesting they give me access.
o Those who receive a request may grant/deny access, on a file by file basis, as they choose.
o Files tab has button "Grant access to all participants", enabled when one or more participants do not have access. Clicking the button gives access to all files shared by this person to all participants.
o Each file has a "..." selection to "modify access". When selected, the list of participants is shown, those who have access are checked. The user can check/uncheck users and click OK to grant/remove access.
This sounds cumbersome, but the predominant use case is probably where a new participant is added, those who have shared files click "give access to all" and voilà - no more Files tab problem.
Evan Cone commented
The whole point of providing chat history to people in the chat is to give them access to all of the collaboration. It seems like a bug to not let them have access to posted Files. Please fix this!