When replicating C4C accounts that share common contact between them to ERP; Multiple contacts are created in ERP (One for each account with which the contact is related).
Reproducing the Issue
Replicate multiple accounts that share a single common contact between them from C4C to ERP. This will in turn generate multiple contacts in ERP; One for each account.
This happens because the SAP ERP system only supports 1:1 Account-Contact relationship, so for every relationship that the C4C account has, multiple ID mappings will be written from ERP when replicated. A new contact will be created in ERP for every C4C related account.
This is an expected behavior.
KBA , LOD-CRM-INT-ERP , Integration of C4C with ERP , How To