

You say you have a wildcard cert but just to make sure: I don’t suppose you’ve used ACME for Letsencrypt or some other publicly trusted CA to issue a cert including the affected name? If so it will be public in Certificate Transparency Logs.
If not I’d do it again and closely log and monitor every packet leaving the box.

My next suspicion from what you’ve shared so far apart from what others suggested would be something out of the http server loop.
Have you used some free public DNS server and inadvertently queried it with the name from a container or something? Developer tooling building some app with analytics not disabled? Any locally connected AI agents having access to it?