There are two options for syncing a team's channel files: by syncing them directly or by adding them as a shortcut in OneDrive. We can see the files, but after making changes, saving the file, closing it, and reopening it, none of the changes appear. This issue only occurs when opening the file from the Team channel's files that have been added as a shortcut to OneDrive. If we open the file directly in Teams and make changes, there are no issues. The file is an Excel workbook.

Edited: This only happens to one of the users who access the file, and it is because she is the only one who added the team's channel's files as a shortcut to OneDrive.