Hello and thanks for the reply.
I’m not sure about the firewall issue. At the moment I have Vaultwarden up and running well.
One time I also had a Subsonic server, and it worked well.
I also have some other reverse proxy rules, they all seems to work: Vaultwarden, subsonic, …
I can’t be 100% sure, but for me I think it’s port related, somewhere on the configuration files. Or maybe something wrong with the install, that I can’t identify…