When a record is being edited in Salesforce at the same time that HubSpot is trying to sync with that record, you'll see an Editing during sync error for that contact:
"We're unable to sync some of your data because it is currently being edited in Salesforce. Please wait until editing in Salesforce has been completed, then try your sync again."
HubSpot will sync with the contact the next time that a sync is triggered. You can also manually trigger a sync for the contact by clicking Resync on the contact's record.