From my knowledge, Synology automatically adds hidden files/folders to its folders, hence Syncthing treats them as non-empty. I have seen at least a few topics on the forum related to this. You may need to use a terminal to actually be able to see (and possibly delete) the hidden files though.
thanks for the hint. I looked at synology folder from terminal. I found a folder called ‘@eaDir’. When I deleted that Syncthing is up to date now. I now need to find a way to disable the creation of that folder by synology. thanks a lot
You may also want to try adding (?d)@eaDir to your ignore patterns. This should allow Syncthing to delete the folder if nothing but @eaDir is left in it.