Hi RJR3! I installed the Projects Hub APP to take a look. With the Grid Report (*New Feature), the image preview doesn't work in either the Project Hub App, or the custom code in your post. Now, toggle Grid Report to "Off". You should view the thumbnails in the table now.
With Grid Report "On" in either your APP, or the Project Hub APP, you need to select "Expand Cell" for each thumbnail which is not the intention. Your code is the exact same as the Project Hub Table::Image Preview Field with the exception of the Field Reference (i.e. [Building Photo]).