Deleted Contact gets restored and create duplicates with Einstein Activity Capture or Lightning Sync

This behavior is working as designed.

When a user is assigned to sync their Contact using Einstein Activity Capture or Lightning Sync both ways, deleting it in only one calendar application causes contact recreation or duplicates in the other calendar application depending on the user configuration settings.

The Einstein Activity Capture and Lightning Sync configurations do not include an option to sync contact deletes when using the both ways direction.

Automatically removing Contacts from Salesforce can impact your sales data. Rather than deleting the Contact in Salesforce, we recommend that the Contact Status field is updated to indicate when a Contact has left a company, is deceased, and so forth. Another option is to manually remove the Contact on both calendar applications if deletion is required.

Note: If Contacts are being synced with the 'All Contacts' filter, the deleted Contact should be wiped out in all Salesforce_Sync Folder of all syncing users to avoid duplicates.

See Also
Stop duplicate Contacts created by Einstein Activity Capture