[Bug Report] Duplicate imported classes

[alexmillane]

Describe the bug

Depending on the order of SimulationApp start-up import of Isaac Lab classes (for example ArticulationCfg), it is possible to end up with objects with inconsistently defined parent classes. For example you can end up with isinstance(FRANKA_PANDA_CFG, ArticulationCfg) ==False

Steps to reproduce

I have made a minimal repro here that contains a failing case, as well as a band-aid that fixes the issue and provides a diagnosis of what is going on, but it not the fix we'd like to pursue.

To run the repro (failing) case:

python scripts/reinforcement_learning/rsl_rl/train.py \
    --task Isaac-Reach-Repro-v0 \
    --external_callback isaaclab_tasks.reach_repro_callback.reach_repro_callback \
    --num_envs 1 --max_iterations 1 --headless

isaaclab_assets_import_error.log

To run the band-aided fix:

python scripts/reinforcement_learning/rsl_rl/train.py \
    --task Isaac-Reach-Repro-v0 \
    --external_callback isaaclab_tasks.reach_repro_callback.reach_repro_callback \
    --num_envs 1 --max_iterations 1 --headless

System Info

Describe the characteristic of your environment:

Describe the characteristic of your environment:

• Commit: tag: v3.0.0-beta2.patch1
• Isaac Sim Version: 6.0.1
• OS: Ubuntu 24.04
• GPU: RTX 5090
• CUDA: -
• GPU Driver: -

Additional context

Add any other context about the problem here.

Checklist

• I have checked that there is no similar issue in the repo (required)
• I have checked that the issue is not in running Isaac Sim itself and is related to the repo

Acceptance Criteria

• Expected behaviour restored: One does not need to mess with sys.modules to fix imported modules.

[RandomOakForest]

Thank you for posting this. The team will review it.