A possible cause is that not all file systems support the same character sets in paths, so syncing can fail due to invalid names. In this syncthing issue, someone mentions that e.g. Hangouts inserts colons in image names: https://github.com/syncthing/syncthing/issues/1734#issuecomm...
Maybe Seafile somehow found a good solution that doesn't cause breakage in other places. Any specific reason you want to switch to them?