To clarify - the response from Support outlines how to handle this issue via Mixpanel's own eventing, but as flagged in my initial question, we use Rudderstack, a CDP, so the above doesn't really answer my questiob.
We were deleting the IPs on the Rudderstack side, but this didn't appear to do anything; we're now trying this with setting it to 0. However, I'm not sure why it wouldn't work by deleting them.
Can I see what event is filling in the IPs? All the events I can see in any given user's activity log all appear to have the right geolocation