Eyedropper issue on double screen setting

While working with an iMac Pro (2017) with a 27-inch (5120 x 2880) Retina display and a Apple Thunderbolt Display 27-inch (2560 x 1440) as a secondary monitor, the eyedropper in Premiere Pro is not working (picking completely random colors).

On the other hand the issue is not happening when the second monitor is not plugged in.

I´ve already tried other solutions offered in this forum but nothing seems to work.

Any ideas is welcome at this point.