Location field not showing map in display form in Esri Maps for SharePoint

[CaraKaser]

I've installed Esri Maps for SharePoint 2013 and all works well except that the "ESRI Maps Location" field does not display a map in the SharePoint display or edit forms. Instead, it's just a blank box:

Using my browser developer tools, I can see that the iframe contains data, but it's just not displaying. Does anyone have any thoughts about why this might be happening?