https://playground.babylonjs.com/#J78BZW#4
Notice as soon as you move the camera, the “middle” block loses all its pixel sizes and goes to 100% 100%.
This only happens when its parent is linked to a mesh, and the other siblings do not share its behavior.
Here is the unlinked version that shows how the item should stay looking visually.
https://playground.babylonjs.com/#J78BZW#2