MC4SF_PICKLIST_OPTIONS_INIT_WARNING

What this means: When mapping a Salesforce checkbox to a Mailchimp dropdown, picklist options could not be loaded for validation. Sync may continue with default Yes/No mapping which can be wrong.

What to do: Review boolean-to-picklist mappings. In Mailchimp, confirm picklist values exist. Refresh audience/mappings. Guide: Field Mappings.