Most of this is used when the textures are not baked as a single instance. Most of the time, you’ll receive a UV passed properly baked but it might happen that because of multiple UDIMs it becomes difficult to manage the rendered UV pass.

Our solution to this is to use the normals (that are not split into UDIMs) and generate our own UVs. You can use this blink script to convert normals to to UV and then use those perfect new UVs to to texture/reflexion work.