Searching WIN10 forums has learned me that loosing focus happens sometimes in various cicumstances.
One solution I have found is adapting a entree in the register.
Run regedit a admin
Search for HKEY_CURRENT_USERControl Paneldesktop
Alter ForegroundLockTimeout (default: 0x00030d40 = decimal 200000)
Set up a higher value: 0x001e8480 = decimal 2000000
Is ten times higher value, and it works fawlesly. Running a scene for more than one hour and then triggering another scene with a keyboard shortcut : Perfect!!
Maybe a solution for other users with this kind of problems!!