This issue was originally identified after sending an email via Acoustic:

CID 4846156 received an email via Acoustic. It appeared in the email greeting as if the last name field was overwriting the first name field. We discovered that there was a third CID (51128128) for this individual. On this third Civi record, the contact's first name and last name were incorrectly swapped. The third CID (51128128) was connected to an email address in Acoustic and was overwriting the first name/last name fields on record for the first CID (4846156).

The email team deleted this individual's record from Acoustic to trigger a reimport from Civi. However, we found that when the contact was reimported to Acoustic, the third CID (51128128) was still overwriting the first CID (4846156) in error. When searching for the third CID (51128128) in Civi, no record can be found. We are uncertain if this record was deleted or deduped at some point in the past.

CIDs for this individual:
4846156 - primary
7425727 - second (do not dedupe)
51128128 - overwriting primary in Acoustic, but no record in Civi (when searching by name or CID, this record cannot be located)

Quick summary: CID 3 is overwriting first name/last name fields on CID 1 when sending email via Acoustic. However, no record for CID 3 can be found in Civi.

Is it possible to locate the third hidden contact record (51128128) and completely delete it to prevent it from overwriting the primary CID (4846156)?