I think I am going to save a lot of lives here, because I have discovered a workaround that fixes the problem.
By using Livia suggestion and checking ArcGIS Online Assistant (which I suggest to use, is very powerful) I doscovered that the real problem is not in the editor nor the app, it is in the MAP!
If you open the map json and scroll to your layer information, you will discover the fields definitions, something like:
{
"fieldName": "NOTE_RISOLUZIONE",
"label": "NOTE_RISOLUZIONE",
"isEditable": true,
"tooltip": "",
"visible": true,
"stringFieldOption": "textarea",
"isEditableOnLayer": true
},
This definition is perfectly correct, but if you scroll to your NEWLY ADDED FIELDS
{
"fieldName": "CATEGORIA",
"label": "CATEGORIA",
"isEditable": false,
"visible": true,
"stringFieldOption": "textbox"
},
See something missing?
"isEditableOnLayer": true
This option is not getting added when you add new fields to a service, thus not working correctly in the Editor Widget
Add that option to true, save the json, open your WAB and shazam!, your newly added fields will be in the editor widget config window.
IMHO this is a BUG and should be addressed by ESRI