This error indicates that the Customer's Recurly Account is missing data in their selected Customer Display name field. You will first want to check the Customer Display Name format that the merchant has chosen under their QBO settings page in Recurly - for example:
We typically see this issue when merchant's have selected Account Company or First & Last Name fields as their Customer Display Name Format. If the field is empty in Recurly, then the record will not sync over to QBO. Therefore, once you confirm what field the merchant has chosen, you will need to check the erring account in Recurly to see if the field is populated and notify the merchant to input the information to resolve.