Sorry in advance; I’ve not looked into this extensively and I can’t at this very minute study Proton’s privacy policy, but here are a few snappy excerpts:
Data collection is limited to the following:
2.1 Visiting proton.me or protonvpn.com website: We employ a local installation of self-developed analytics tools. Analytics are anonymized whenever possible and stored locally (and not on the cloud). IP addresses are not retained and stored for such analytics.
But are they stored for other reasons?
IP addresses, email addresses, and phone numbers provided are saved temporarily in order to send you a verification code and for anti-spam purposes. The period of temporary data retention is determined by our legitimate interests of protecting the service…
2.5 IP logging: By default, we do not keep permanent IP logs in relation with your Account. However, IP logs may be kept temporarily to combat abuse and fraud, and your IP address may be retained permanently if you are engaged in activities that breach our terms and conditions (e.g. spamming, DDoS attacks against our infrastructure, brute force attacks).
So Proton can choose to save IP addresses for frivolous reasons, such as a supposed breach of their T&Cs?