When a new user registers through the mobile app, and the ContactKey isn't immediately set, the MobilePush SDK assigns a temporary identifier (a GUID) to the device. This results in the creation of a new Contact in Marketing Cloud. Once the user's information is synced from Sales Cloud and the ContactKey is established, the device can be correctly associated. However, until this association occurs, the system treats the device as belonging to a separate, anonymous contact.

Tracking Extract, run as an Automation Studio Data Extract Activity, is the documented mechanism for pulling detailed, per-send delivery status data - including records marked as Not Sent - for journey-driven email sends. Unlike the standard Sent Data View, which primarily reflects records that were successfully processed for sending, Tracking Extract exposes the fuller set of delivery outcome codes, including exclusions and failures, giving the granularity needed to specifically isolate and report on the ' Not Sent ' population from journey emails. Option A, querying the Sent Data View, is not reliable for this purpose because that view is generally populated with records that were successfully sent, not the ones that were excluded or failed to send
- it is the wrong data source for isolating non-sends. Option B references a ' Subscribers Not Sent to ' standard report, which is not a real, out-of-the-box Marketing Cloud report name. Option D, Analytics Builder Intelligence Reports, refers to a different reporting layer focused on broader engagement and journey performance visualizations rather than granular per-record delivery-status extraction, and is not the documented tool for this specific ' Not Sent ' reporting need. Reference: Tracking Extract, Automation Studio Data Extract Activity.

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.