Well, I hate to be this person, BUT..
IS ANYONE ELSE HAVING PROBLEMS PUBLISHING LAYERS IN A WEBMAP? OR WEBLAYERS?
To me, it feels like since they updated AGOL this month, some of my layers that used to publish seemlessly are now not loading, with an error that says "Unable to add layer. Feature layer must be created with either a URL or a source". If I export the feature class to a new dataset, it publishes. I can change the fields around and it will publish, but the second I import symbology to the layer - "Staging Failed" when trying to test publish web layer.
So so frustrating. Why can't I publish a layer with imported symbology? Even before I started importing symology on exported datasets ... suddenly my layers stopped publishing. Yea the layers were renamed (just the alias!) but this is too much.