i see yes that is why i told we have problem with scene load
that not happen in shadermaterial
https://www.babylonjs-playground.com/#UXCB15#67
simple custommaterial is work well
https://www.babylonjs-playground.com/#UXCB15#68 (new Object don’t have Uv? )
https://www.babylonjs-playground.com/#UXCB15#69
i find bug 
when you use new Uniform that not set for all instance when you update that
https://www.babylonjs-playground.com/#UXCB15#70 ( make pos.xz uv)
https://www.babylonjs-playground.com/#UXCB15#71
i don’t know where we can fix it need someone have time and check why when we define new Uniform that not update for all mesh