Hello LastPixelBorn and welcome to the ArtRage forums
Thanks for the screenshots and video! Always so much better than relying just on words!
Sadly, whilst I would love to be able to say why that is happening for you, unfortunately so far I can in no way reproduce what you are seeing there.
But I do have of some more questions!
Which exact version of ArtRage6 are you using?
Dose this happen when using a mouse or trackpad instead of the Wacom?
And do you have the latest Wacom Mac driver: 6.3.38-3
Also…
Dose this “offset” happen when sampling colours from different parts of the actual painting?
Is this happening with just this reference image or other reference images?
Is this happening in just this painting? or all paintings?
Is your screen a Retina screen?.
Is it a second connected monitor, comparable to a Retina screen or with higher or lower pixel density?