I reply to my own post adding some details.
I have another NUC, Hades Canyon (NUC8i7HNB) with AMD Radeon RX Vega M GL video card and the sames happens with Xorg / x11 (Wayland disabled).
It's 3 months I have reported this bug, other users have reported the exact same problem and there is no clue on what's happening.
This is VERY frustrating and annoying because every time I leave my PC I risk loosing all my work.
Marco