A correction to my previous answer, I hope this can be helpfull to whom will face this issue in the next days.
It is true that ArcGIS PRO started after Dan's suggestion, but next day i had the same problem.
I didn't mention that I was working on W10 and I was aware of complatibility issues but the fact is that when I moved to W10, in December, PRO worked properly since then till one week ago. Then something happend.
Anyway, the definitive solution was moving to PRO 1.2.