Because the Marketing Cloud Connect app-level connection itself reports as successful, but Sales Cloud objects still fail to appear or synchronize within Contact Builder, the most direct and efficient troubleshooting step is to verify that the specific users involved in the integration — both on the Marketing Cloud side (the integration/API user) and the Sales Cloud side — hold the correct permission sets and role-based access required to expose and synchronize Salesforce objects into Contact Builder, since a successful app connection does not automatically guarantee sufficient object-level and field-level permissions for synchronization to function. This is a targeted, low-effort first diagnostic step consistent with standard troubleshooting methodology: verify permissions before escalating to more invasive fixes. Option A, sending a test email to validate tracking, addresses a different layer of the integration (send-tracking sync) rather than the object-visibility issue described in Contact Builder specifically. Option B, creating new users and reinstalling entirely, is a drastic, high-effort action that should only be considered after simpler causes like permissions have been ruled out. Option C, validating Sales Cloud users have BU access, is narrower and less complete than validating permissions across both platforms, which is the more thorough and correct first diagnostic. Reference: Marketing Cloud Connect Troubleshooting, Contact Builder Salesforce Data.