Can't add Entity Reference

I tracked it down to the Demo Admin module.

What is the issue with the Schema.org Demo Admin module? Is it something we can fix?

I wanted to add an entity ref to Article for Person that is the author. I haven't figured out how to add the property 'Author' yet, but I first need to add the entity ref field. When adding a new entity ref field the save would get hung up.

You need to adjust the default properties for 'Article' to include 'author' via 'Default Schema.org type properties' (/admin/config/schemadotorg/settings/types)