What causes a sync from Salesforce to Marketing Cloud Account Engagement?

The main cause of a sync from Salesforce to Account Engagement is making field changes to a Lead

or Contact record (D). This will trigger a sync of the updated fields to the corresponding prospect

record in Account Engagement. Updating a formula field in Salesforce (A) will not cause a sync, as

formula fields are not supported by Account Engagement. Updating a field on a Contact record that

does not have an email address (B) will not cause a sync, as email address is a required field for

syncing. Opening a one to one email © will not cause a sync, as it is not a field change event.

Reference: What Causes a Prospect to Sync from Salesforce to Account Engagement?