Physics callback problem?

Hello, i am creating a forest environment to combine with pegasus.simulator. So when i first load a scene in Isaac I can spawn the drone. I save this and go to USD composer to add environment elements. When i come back with the file to isaac sim, and try to spawn the robot i get this error

2024-04-26 14:04:06 [204,087ms] [Error] [asyncio] Task exception was never retrieved
future: <Task finished name='Task-3512' coro=<UIDelegate.on_load_vehicle.<locals>.async_load_vehicle() done, defined at /home/maciek/Desktop/PegasusSimulator/extensions/pegasus.simulator/pegasus/simulator/ui/> exception=AttributeError("'NoneType' object has no attribute '_physx_interface'")>
Traceback (most recent call last):
  File "/home/maciek/Desktop/PegasusSimulator/extensions/pegasus.simulator/pegasus/simulator/ui/", line 222, in async_load_vehicle
  File "/home/maciek/Desktop/PegasusSimulator/extensions/pegasus.simulator/pegasus/simulator/logic/vehicles/", line 77, in __init__
    super().__init__(stage_prefix, usd_file, init_pos, init_orientation)
  File "/home/maciek/Desktop/PegasusSimulator/extensions/pegasus.simulator/pegasus/simulator/logic/vehicles/", line 105, in __init__
    self._world.add_physics_callback(self._stage_prefix + "/state", self.update_state)
  File "/home/maciek/.local/share/ov/pkg/isaac_sim-2023.1.0-hotfix.1/exts/omni.isaac.core/omni/isaac/core/simulation_context/", line 607, in add_physics_callback
    ] = self._physics_context._physx_interface.subscribe_physics_step_events(callback_fn)
AttributeError: 'NoneType' object has no attribute '_physx_interface'

Could you shed some light on why this could be the case ? I on purpose first try the drone in the Isaac sim to be certain the physicsScene is there, save that satge, load in usd composer, and when it comes back there is this issue.

Best regards,

@maciek.jankowski989 i am just another OV user and have not worked with the pegasus simulator in the past, so take my input lightly. looking at the log report above, it looks like something that was added in Composer that then got brought back into Isaac Sim has caused a missing physx attribute. however, i am not sure if it has anything to do with the physicsScene prim.

to work around this, i wonder if you could create the environment independently from the Isaac Sim scene and then reference that environment back into Isaac as either payload, reference, or a new layer. that way you don’t need to bounce between the two apps and bypass any discrepancies that may be introduced by doing so.