Account Name Removed from Salesforce Contact by Lightning Sync or Einstein Activity Capture (EAC)

This article explains why a Salesforce contact's Account Name is unexpectedly removed or cleared by an automated process. This issue is most likely caused by Lightning Sync or Einstein Activity Capture (EAC) syncing contacts bidirectionally (two-way) across multiple Salesforce orgs or sandboxes that share the same connected email account.
Einstein Activity Capture (EAC) is a Salesforce feature that automatically syncs emails and calendar events between Salesforce and external email services such as Microsoft Exchange or Google Workspace. Lightning Sync is a predecessor feature that syncs contacts and events between Salesforce and Microsoft Exchange.

Common Causes

Cause 1: Multiple Orgs Using EAC with Bidirectional Contact Sync

The same email account is connected to two or more Salesforce orgs (including sandboxes), and EAC is configured to sync contacts in both directions. When a Salesforce Account does not exist in one of the orgs, the sync removes the Account Name from the contact across all connected orgs.

Cause 2: Multiple Orgs Using Lightning Sync with Bidirectional Contact Sync

The same email account is connected to multiple Salesforce orgs with Lightning Sync configured to sync contacts in both directions. When a matching Salesforce Account is not found in one org during a sync cycle, Lightning Sync removes the Company field from the Microsoft contact, which in turn removes the Account Name from the Salesforce contact.
Important: If bidirectional sync is configured, Salesforce recommends that admins create the relevant Salesforce Accounts before enabling contact sync. If unmatched contacts are not resolved before the next sync cycle, Lightning Sync removes the Company field from the Microsoft contact.