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 ID mapping for the ERP contact is written on the business partner relationship. So for every relationship the account has, multiple ID mappings will be written in ERP when replicated. A new contact will be created for every related account.
This is an expected behavior.
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