Hi,
I am using the "add Shapefile Widget" that someone here helped to create. Now that I am using it and checking the behavior I notice that the polygons that compose the shapefile, after adding it to WAB app the polygons do not respect the original forms, they have a distotion very significant.
First I thought it was because AGOL use Web Mercator Coordinates system. Here in Puerto Rico we use Nad83 Projected Coordinate system So I added on parcel example in Nad83 and I notice the distortion, after that I added the same chunk of parcels projected to Web Mercator and I had the exact same distortion in the same parcels.