Google (Gmail) Contacts / iPhone Sync

For the last six months, I've been having a problem with the contact information for one person (always the same person) not syncing between Google Contacts and my iPhone.

I can "force" the sync by going to Settings>Contacts>Accounts>Gmail>Contacts—toggle the contacts off/on. This works for an indeterminate amount of time, and then the same person disappears AGAIN. Interestingly - to me at least - I cannot create a contact directly on the iPhone either. When I search, their name comes back via "Siri Found in Apps," and I attempt to either create a new contact or add to an existing contact, it won't work.

It's like their name/phone number is hitting some weird bug that makes it unrecognizable.

The phone number is a US mobile number.

iPhone Model - 13

iOS Version - 17.3.1

Any help solving this weird mystery will be GREATLY appreciated.