No, these are actually errors that cause cook failure in the editor and in Jenkins. I (and many others by the number of posts I have read concerning it) have encountered it on a consistent basis.
This problem is a product of how Unreal handles structures and apparently will never be addressed by Epic.
Additions to an existing structure (in this case the Inventory Item structure) do not propagate through blueprints. This may be by design but it is certainly annoying as the error does not show up in PIE, only when you attempt to cook the project.