This can happen if there is incorrect linkage between data items, specifically, if a loop is created in the properties of your data item. For example if you have a data item for an article and you want to include the URL as the “mainEntityOfPage” a loop can be created if the URI and the URL in that field are the same. This means that our system believes you are trying to link the data item to itself, rather than the URL. 


This has an easy solution. Change the URI so that it is the URL and add an #anchor to the end. This will distinguish it from the URL itself. Check the other fields and make sure not to link the data item you’re working on, to itself. 


If you are having trouble after checking the properties for the data items, please contact support@schemaapp.com and we’ll be happy to help you figure it out.