Why does the re-shaping edit widget not work on all web applications?

[TomLambert]

I have generated a web application which enables tabular and spatial data to be edited (in ArcGIS Online)

My process consists of uploading the layer by publishing a service, enabling the layer to undergo all edits in the Feature Layer options.  Create a web map and finally a web application, again enabling edits.  I made several of these apps and they worked just fine enabling of the polygon and suddenly in it has become difficult to re-shape the polygon, although the create new polygon and editing of certain attribute fields.  In the below image is a picture of what sometimes does not happen - when the vertices appear enabling editing of the polygon.

Why in some cases this function works and in others it is not possible?