I have just reviewd our staff contacts within Hubspot as we keep them for a lot of testing and the exact same thing has happend to us. Neither contact has been merged together the contacts are simply connected via email.
The emails are completely unrelated (@tmaclub.com) & (@select-mortgages.com).
As there is no way to unmerge a contact how do we separate the email address and keep all relevant information on each concact? We have never had this hsppen before and i have reviewe the activites for the dominant email address and there is no visible commmection.