I've often seen files that are uploaded into Teams to a Chat (not conversations - those are fine) stop working. Teams will report to me or the recipient that it cannot find the file.
I just noticed in my OneDrive for Business folder for Sharepoint sites, which is what sync's files for Teams, is a folder called "Microsoft Teams Chat Files" with a bunch of files I've shared, but that folder is not sync'd. I never unsync'd it, didn't create it, and have no idea how to go about making sure it stays sync'd, or even know if it needs to be sync'd.
I thought this might be part of the issue I see where files just stop working in the Chat sessions.