I think Mullvad was being used for a lot of CSAM torrenting, and they didn’t like that. They got tired of regular users complaining of being blocked everywhere, and Interpol knocking on their door.

Unfortunately port forwarding also allows avenues for abuse, which in some cases can result in a far worse experience for the majority of our users. Regrettably individuals have frequently used this feature to host undesirable content and malicious services from ports that are forwarded from our VPN servers. This has led to law enforcement contacting us, our IPs getting blacklisted, and hosting providers cancelling us.