Traffic mismatch. Contact added to another contact
Traffic mismatch. can happen due to many reasons. e.g. forwarding emails meant for someone else and clicking links. or filling forms with someone's else details.
To sort this issue contact that causes a problem needs to submit an SS form. It will re-establish the tracking
Or you can disable the problematic's contact device from a contact it was added to by going to the contact's membership tab, clicking devices, and disable tracking for the problematic contact