Upon auto-conversion from lead to contact fields are erased - Help
I am experiencing an issue where a 3rd party program within SFDC helps auto-convert leads to matched target accounts to contacts. Upon conversion a few key fields are overwritten with blank values.
When I look at the reason it states "Synced from salesforce.com Contact ID: XXXXX"

How can I prevent SFDC from overwriting the field value with "null"?
What I tested:
I tried blocking field updates on the field by checking SalesForce Sync but that prevents marketo from updating the field.
I tested the standard conversion of Leads to Contacts within salesforce by clicking the convert button and the field information carries over just fine.