IIRC from running into this same issue, this won’t work the way you have the volume bind mounts set up because it will treat the movies and downloads directories as two separate file systems, which hardlinks don’t work across.

If you bind mounted /media/HDD1:/media/HDD1 it should work, but then the container will have access to the entire drive. You might be able to get around that by running the container as a different user and only giving that user access to those two directories, but docker is also really inconsistent about that in my experience.