Esri tech support said Relates are not supported in Short List. I am using the beta AGOL Builder. Until they do we will have to routinely permanently join our data in to the feature class. It is perfect for things like Capital Improvement Projects viewers. Also it does not display the attribute's actual field name, just the raw attribute data, from the popup. I will have to store the attribute field name in the actual attribute, with a field calc. That is the only workaround I can think of and am about to test. Future Enhancement to Shortlist? Once these are implemented it'll be perfect for our public projects viewers!