[PyT DTensor]Qwen/Qwen3-30B-A3B fails due to assertion error

**Describe the bug**

```
assert tokens_left_for_obs >= 0, (
```

**Steps/Code to reproduce bug**

```
uv run ./examples/run_grpo_math.py --config examples/configs/recipes/llm/grpo-qwen2.5-32b-32n8g-fsdp2tp8sp-actckpt.v3.yaml grpo.max_num_steps=1000000 grpo.val_period=10 policy.max_total_sequence_length=4096 policy.model_name=Qwen/Qwen3-30B-A3B policy.tokenizer.name=Qwen/Qwen3-30B-A3B policy.dtensor_cfg.tensor_parallel_size=4 policy.dtensor_cfg.sequence_parallel=False policy.dynamic_batching.enabled=True checkpointing.enabled=false logger.wandb_enabled=true logger.monitor_gpus=true
```

**Expected behavior**

A clear and concise description of what you expected to happen.

**Environment overview (please complete the following information)**

- Environment location: [Bare-metal, Docker, Cloud(specify cloud provider - AWS, Azure, GCP, Collab)]
- Method of install: [pip install or from source]. Please specify exact commands you used to install.
- If method of install is [Docker], provide `docker pull` & `docker run` commands used

**Environment details**

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Otherwise, please provide:
- OS version
- PyTorch version
- Python version

**Additional context**

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