A number of OneDrive users were recently impacted by an update to the app that dropped support for non-NTFS file systems. While at the time it was unclear if this was a bug or intentional, Microsoft has now confirmed in a statement the move was done on purpose.
In a statement to Neowin, Microsoft says:
Microsoft OneDrive wants to ensure users have the best possible sync experience on Windows, which is why OneDrive maintains the industry standard of support for NTFS. Microsoft discovered a warning message that should have existed was missing when a user attempted to store their OneDrive folder on a non-NTFS filesystem – which was immediately remedied. Nothing has changed in terms of official support and all OneDrive folders will continue to need to be located on a drive with the NTFS filesystem.
The major issue with the change was that there was no warning ahead of time, leaving anyone using a drive formatted in a file system other than NTFS high and dry following the update. If the drive you’re using to store your OneDrive files if formatted in another file system, such as exFAT or FAT32, you’ll have to reformat the drive as NTFS and re-sync your files.