Due to terraform's concurrency, and that the Mullvad API (a) doesn't allow specifying a port number to create; (b) doesn't include the generated port number in the response, we can't determine the port value (or terraform ID) if more than one mullvad_wireguard_port resource is created concurrently.

Hopefully there is some way to lock around a CreateFunc, but I'm unfamiliar with Go and haven't found an easy way yet. (Ideally there'd be something in the terraform SDK.)