PixarAnimationStudios
Hydra scene index mode doesn't resolve UDIM paths
Try to render the attached scene with USDIMAGINGGL_ENGINE_ENABLE_SCENE_INDEX=1. If you start the render process from some directory other than the one containing the USDA file, the UDIM maps will not be found (if the cwd for the process is where the USDA file is, chances are the renderer will find the UDIMs using the unresolved relative paths).
I can see no evidence that when using scene index plugins that UDIM paths are run through UsdShadeUdimUtils::ResolveUdimPath as they are when using the legacy hydra delegate.
If this is not currently on your radar to be fixed for 25.05, I can try to come up with a PR.
This is the first I've seen this, although it doesn't look too hard to fix. I'll gladly accept any PRs though!
We could consider specializing UsdImagingDataSourceAttribute<SdfAssetPath> to check for the "<UDIM>" string and call this; or have UsdImagingDataSourceMaterial wrap asset parameters and call this... While I don't particularly expect UDIMs outside of shader inputs, there's something nice about handling it uniformly in our baseline asset path handling. Let me know what you think!
Regardless, we'll try to address this for 25.05. It seems relatively high value for effort.
Just adding a comment to make sure you see that I did submit a PR for this...