When using the same attribute in multiple groups, it is strongly advised to use only one of these groups for the same product afterwards.For example an attribute Resolution with terms like Full-HD or 4K could be part of a group Screen (like the resolution of a monitor), but also of another group Cam...
Adding an attribute group with an already deleted attribute (without saving in between) doesn’t re-add it at the moment. Simply reload the product edit page, re-add the desired attributes or groups again and you’re good to go.
