Decal slide on AR Foundation

[kingbaggot]

Decals work fine in the game window preview but "slide" on AR builds. Video attached.
Only the white text reading "" is a decal in this clip - the other text is on the models texture map.
Initiailly the model is being rotated, and then after that I'm moving the camera around the car while it is static.

https://drive.google.com/file/d/1O6fFYCriEl8RjQ6lFBBt2n4hftrTpO5B/view?usp=sharing

The decal cubes are children of the car model so I don't see why their effect would change this much.
I'm using Unity LTS 2019.4.32 w. ARFoundation 4.0.1 - and running on a google pixel 2.

any help much appreciated :)