Well I'm kind of ashamed to say it but I gave up, I spent far too many hours on this one (felt like ~25 between the last three days) just on this one single issue in order to avoid an IP block for my clients as Microsoft was blocking the IP of the host machine, and I still couldn't get it to work. I eventually opted instead to create a new Public Cloud instance at OVH instead, migrated all the data to it, using the floating IP, and things seem to be working fine now (only accessible with one public IP address so Docker had no other choice, lol). Sorry there's no confirmed solution to this one.