In After Effects, the position property of a layer is always calculated relative to its anchor point. When you move the anchor point of a layer, it changes the reference point for position calculations.
In your initial setup, with the anchor point at (540, 540) and position also at (540, 540), the layer is centered in the composition. This means that the position is calculated based on the center of the layer relative to the composition.
When you change the anchor point to (0, 540), but keep the position at (540, 540), the layer's content shifts right by 540 pixels. This shift occurs because the position property is still calculated relative to the anchor point. So, even though the position remains the same, the visual position of the layer changes because the anchor point has moved.
In essence, After Effects calculates the position property based on the distance between the anchor point and the layer's content. When you move the anchor point, it changes the reference point for this calculation, causing the layer's visual position to shift accordingly.
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