The environment:
Hp Envy.
Version 1803 (OS Build 17134.48).
All available updates applied to the OS and the Windows apps.

The issue:
Ever since I updated the OS to 1803, I get this fuill screen Cortana windows (with an "X" in the upper right corner.)
I can't seem to predict when it will appear, but when it does it is always during a period of non activity on my laptop.
If I'm using the laptop, I never see it.

My screen saver is set to display the time after 120 minutes.
And that much inactivity does not take place before this Cortana window appears.

Is anyone else experiencing this ?

And more importantly (to me), does anyone know what to do to get this to stop ?

I suspect, but can't prove this Cortana windows is something new.

Thanks in advance for replies, all.