Hi oristides,
I also now have tried the Professional Edition with API services enabled and as you say the problem disappears.
I have flagged this with the Microsoft Team who are still in the process of assisting me
However at around $40AUD per user per month to have this enabled (and all users must have it if just one person needs it) it doesn't make financial sense to do so, I'll just use Power Update to push the PowerBI desktop file to PowerBI.com as often as needed.
I will let you know Microsoft's response