If the files were 100% in sync before you set up syncthing, then it may look like syncthing is transferring files while it actually is not. In an initial sync it sure as hell shouldn’t delete any files, because that wouldn’t make sense. Are you sure this is happening, i e can you actually see it in the folders or is that just the way you interpret the gui?
If the folders were not in sync but share mostly the same data with one folder being more recent, read this thread from 4 days ago
