Hey Frederico,
Front window is broken presently in the Keyboard Maestro action.
BUT -- I was able to substitute the window frame of the front window in Chrome instead.
Google -- Find Image in Front Window Tests.kmmacros (27 KB)
I tested with click found image as well, and it works.
I'm testing with the newest Chrome Beta on macOS 10.12.6.
Google Chrome Beta -- v70.0.3538.22 (Official Build) beta (64-bit)
I only have 1 screen, so I can't be sure how it will work with 6.
I think as long as you're working in the front window you'll be okay, but you'll have to test to be sure.
-Chris