Select the duplicate contact and make merge all the information to one account. All related objects will be added to this newly merged contact.
This functionality uses a setting called "contactDuplicateFinder_
|Find Duplicate Setting|
|To add/remove fields use this KEY:||contactDuplicateFinder_
It can be seen that Owner.Alias is set to be searched also. However, fields in the Owner object are not accessible and that is the reason for the error message. So, in order to fix the error, this field must be removed from the Setting.
In order to solve the business request, new custom lookup field of type User needs to be created in the Contact object and this field should have the same value as onwer field. This way, owner's fields will be visible over this new helper field and can be put into Setting.