I am investigating some Marketo Salesforce sync issues where many duplicates are being created in Salesforce from a single lead in Marketo. This happens has happened on several unique dates from a list import, but not for all leads on the list. This issue is not related to Contacts in Salesforce, all duplicate records created are Leads.
8:42 - Top Row: Marketo creates the Lead from the list import
9:01 - Second Row: Salesforce creates the first Lead - Person Source = List Import
9:07 and 9:24 - Top Row: "Error updating Sfdc lead id after crm creation. Leads might have already been synched."
9:39 - Top Row - Marketo inserts original Lead into Salesforce
Any ideas? Here is the activity log for the first two rows: