This particular error basically means that we're unable to sync a HubSpot contact because the corresponding lead or contact has been deleted in Salesforce. The error is harmless in that it does not prevent any data from syncing, but is a good indication that HubSpot and Salesforce might become out of sync over time.
To fix this, navigate to the contact in HubSpot that is not syncing to Salesforce. Scroll until you see the Salesforce Sync section on the left-hand side of the contact record. You'll see a message here indicating that this contact is no longer syncing with Salesforce. Click Resync to attempt to sync the contact. If a corresponding record is not found in Salesforce, HubSpot will create a new record.
If you would like to prevent this from happening in the future, please follow the directions noted below.
- Navigate to your Account Menu > Integrations.
- Under the Salesforce Integration, click on Settings.
- Scroll down to Delete in HubSpot when deleted in Salesforce and select the appropriate check-boxes. When ready click on Save.