Hi, Marco
I'm the one of many who like the video you recorded and the workflow you conducted.
Did you check the utility service setting at your ArcGIS Online site configuration?
[ATTACH=CONFIG]32665[/ATTACH]
It is automatically set up with ArcGIS online printing services for all clients/applications that utilized via ArcGIS online to enable printing. If it has been changed by accident, you may need to change it back to the default.
Would you please let us know the progress? I would like to test with my setting with portal for arcgis.