If you need precise values for data (VertexAnimationTexture for example), better way to check correctness of the sampled values with a “DebugFloat3Values” node in material editor.
Because if you are checking values from the screenshot there are multitude of things that come into play. For example here:
This means that by default viewport in Unreal Engine has bunch of PostProcessing effects going on. One of the ways is to use your own PPV and remove as much effects as you can, but the point is things get tricky when rendering pixels.