There's some things posted here by a (now former) Certbot engineer describing the intention of the "public ip logging" feature and that it wasn't ever actually implemented:
For your own ACME account, if you request the ACME account object from the server you can get the IP that originally created the account. (Though, I don't know as any popular ACME client easily exposes that information.) But it's only accessible to the holder of the account key directly, and to people working for Let's Encrypt, not to the public in general.