I like to organize my movies by year/name, e.g. "Library/Movies/2019/Movie name (2019)/".
When i set Movie folder pattern to "%my/%mn (%my)", the slash gets replaced by a space, and the movie gets sorted into "Library/Movies/2019 Movie name (2019)/".
Not sure what the best way to solve this is, but i don't think slash should be considered an invalid char for this pattern.