That comes up when there isn’t a value for name to display. So if investor is a label for the company field, then the company record name field I would expect to find empty.
Actually, due to REST still being developed, that may not be the best approach (though it normally would be). Try using the Company endpoint to first create the complete company record and retain the id. Then, when you create the contact, use that new company id.
Yes that’s exactly what we do. We add the company using the xml-rpc and then we use that ID to as the company ID when we create the contact using REST?
Have you tried removing company name and just providing the id? Not sure if that would work but it would be something I would normally attempt to find out?