Two distinct root causes commonly prevent click tracking from correctly writing back to Salesforce Contact records. First, using Email Address as the Subscriber Key (A) can cause identity-resolution mismatches between how Marketing Cloud identifies a subscriber for a given click event and how Marketing Cloud Connect attempts to match that event back to the corresponding Salesforce record ID — if these two identity schemes don ' t align cleanly, the tracking data has no reliable path back to the correct Contact record. Second, Individual Level Tracking must be explicitly enabled in the Marketing Cloud Connect configuration for click (and open) events to be captured and associated at the individual subscriber level and written back to Salesforce at all (C) — without this setting selected, engagement data is not tracked with the granularity required for record-level write-back, regardless of Subscriber Key configuration. Option B, using ContactID as Subscriber Key, is actually a recommended best practice for reliable Salesforce record matching and would generally support, not hinder, correct click write-back — making it an incorrect cause. Option D, a 15-minute sync interval for Synchronized Data Sources, describes normal, expected latency for data synchronization and is not a cause of clicks failing to appear at all. Reference: Marketing Cloud Connect Individual Level Tracking, Subscriber Key Best Practices.