Robots explode when num_envs is more than 2

[mamoruoka]

I am trying to execute InHandManipulationTask using a custom robot. I converted the robot urdf to usd file and added task files such as config files, task file, robot file, and so on.

When I started the train simulation with num_envs greater than or equal to 2, all robots gather at env0 robot and explode. When I started the train simulation with num_envs equal to 1, simulation continues successfully.

I confirmed the following.

• converted urdf to usd without checking "fix base link"
• articulation root is set at the root link of the robot
• the robot is fixed in space by empty Xform and fixed joint
• all robots are located at the center of env just before train simulation begins
• [Error] [omni.physx.plugin] PhysX error: Illegal BroadPhaseUpdateData is shown and the simulation stops when used cpu
• succeeded to execute multiple envs in sample simulations such as AllegroHand, CartPose.

What should I do to simulate in multiple envs?

[mamoruoka]

I solved this issue. I converted urdf file without checking "fix base link" in Isaac sim ver 2023.1.0-hotfix.1 and added fixed joint under top-level prim of the robot, which connects the root link and empty.