Bottom Line: I believe ESRI moved the location of the default map that displays when a new app is first created in Web AppBuilder 2.0 DE. Any applications that were relying on that map can no longer access it and display nothing in the map area when editing and a basically blank screen when launched. Adding the Topographic map from ESRI's Living Atlas should solve the problem. (Map > Choose Web Map > Public > ArcGIS Online > row 1, column 4) I don't know if this will help anyone, but I thought it worth sharing. It took me a little time to figure out what was going on with some of my apps. Especially since I had been working almost exclusively with the default map (for customization and testing) for quite some time.
