Cesium for omniverse with Issac Sim 2023.1.1

I have installed omniverse extension and followed the steps mentioned on i) Quick Start and ii) Adding Cesium To Omniverse Application.

I could generate a terrain in Omniverse USD composer and saved the resulting usd file to local nucleus store. I am trying to use this usd file inside an application in Isaac Sim. I am launching the application using ISAAC_PYTHON on command line. I am using following code to reference the usd file in the app’s world/stage.

prim = world.stage.DefinePrim("/World/layout")
prim.GetReferences().AddReference(cesium_terraion_usd_file_path)

There are no errors while running the above code. But in place of the terrain, I can just see a black screen in the viewport. Camera sensors in the scene are capturing black images.

Any pointers to debug this issue will be very helpful. I could not find many references to how to make Cesium and Isaac Sim work well together. Thanks