Why do some files seem to change on every sync?

If you’re unsure why a file is listed in the confirmation dialog, either double-click the file or open select Get Info from the context menu, and compare the file attributes between source and destination: the modification date or size should be different. For additional help, see Sync confirmation dialog.

Old volume format (FAT32)

The default overwrite policy is “Overwrite if timestamp or size is different”. This option can be changed in the sync settings Destination tab. Most volumes work out of the box with this default setting, but some volume formats may cause files that have not been modified between syncs to be listed again in the confirmation window. For example, volumes that use the FAT32 file format (which is primarily used by older devices) don’t seem to support custom modification dates for directories, even though there’s no official documentation on this behaviour. It seems that whenever a directory is created, the current date is automatically set and cannot be changed. Hence SyncTime will find that the modification date of a source directory is always different from the one on the destination, trying to sync it each time. A workaround is to use the “Overwrite if source file is newer” overwrite policy instead. Beware that when using this overwrite policy, if you replace a source file with another version that has an older modification date, this change won’t be synced until you open and modify the source file so that its modification date is updated.


When you sync to another computer, such as a network attached storage (NAS), it can happen that the modification date of a copied file is reset by the destination operating system, which may cause subsequent syncs to report that the file still needs to be synced. In some cases, the problem can be solved by making sure that the network volume has both SMB and AFP services enabled and it is mounted with the same username as the account that you’re currently using on your Mac.

Unreliable network protocol implementation (FTP / WebDAV)

Apple’s FTP and WebDAV implementations have issues that may cause files to be synced unexpectedly because their modification date or size is reported to be different than what it actually is, or attributes (such as the creation or modification date) of the file are copied incorrectly.

In an official post on their developer forums, Apple acknowledges that FTP support is slowly disappearing in macOS and discourage from using it: https://developer.apple.com/forums/thread/97469

While Apple doesn’t have an official topic about WebDAV, there are user reports on the internet about issues: https://discussions.apple.com/thread/252944603?sortBy=best

If possible, try to use SFTP (as mentioned in Apple’s topic about FTP) or SMB.