There are several posts that pertain to hiding the error message that is displayed when opening a Web AppBuilder app that references a layer that is unavailable. The offered solution is to comment out the relevant code in MapManager.js.
I would like to know how one might make this the default behavior in all circumstances which would include when opening the viewer in Portal and when creating new apps in portal. I see no global setting and presume this would require making code changes in Portal somewhere but I have been unable to locate where.