You might have setup something wrong then. It should work. The problem with torrenting on 1 server and saving the data to another directly via smb/NFS is that every write is at the behest of uploading to that network storage.
What would be better might be that you:
add categories
mount /completed/tv/ as a network share to hetzner-storage
then only when the torrenting is done does it auto copy the data to the SMB share
I have this all done internally. I torrent on one box, it’s finished and gets moved via NFS to the storage server. Which sonarr/radarr file away. They notify jellyfin to resync the library. The jellyfin box has the storage box mounted via NFS.
If you can test with small files, IE copy a 100m file onto the SMB share and then see if that was replicated to the storage box then you will have the basis of the solution.