"Related To" is blank for event synced with Einstein Activity Capture

Related To (What) Field

EAC sync does not populate the 'Related To' field of an Event. This field is used to specify a 'What' relation on the event, but sync does not associate events to 'What' records (Accounts, Opportunities, etc). For instance, if you add an Account or Opportunity to an existing Outlook calendar event, that relationship won't carry over to the synced Salesforce Event.

Name (Who) Field

EAC event sync can perform 'Who' associations, specified in the 'Name' field of the event, to Contact or Lead — but only when the event first syncs to Salesforce and is inserted. Who association processing does not happen on event updates.