Bug when running script on different computer

Running on macOS Sierra 10.12.2
PsychoPy v1.84.2

When I run on my macbook air with the above parameters - no issues.

When I run on my lab’s macbook pro I have a bug. My fixation crosshairs come up while stimuli are still on the screen. This second computer is running OS X El Capitan 10.11.5 and PsychoPy v1.84.2.

Any thoughts why there would be a bug on one machine when it works on the other if they are running the same version of PsychoPy? Could it have anything to do with the different OS?

Updated the macbook pro to macOS Sierra and problem went away.