We are still on EE3 version as EE5 migration is still ongoing due to our heavily customized site.
Our system admin has received numerous emails from the EE3 system advising of Registration Confirmations. However, they are from past events going back to 2019 so they aren’t factual or based on new live events. These legacy events are also deactivated or past the date in the system.
Our developers have investigated and suspect the issue comes from the core EE plugin.