I just scored a 9… and on a hunch, re-took it on my Note 8. Scored a 0 there.
Crappy monitor… Some of those squares just looked the same. Put them next to each other, and saw a double-wide block of the same color. So monitor will definitely play a role.

In the past, my wife and I have taken these tests. She’s never not scored a 0, I’ve scored close to 0 but not always at zero.