CUDA Illegal Instruction in test_k_grouped_gemm_contiguous

I encountered a CUDA kernel error while running the `test_k_grouped_gemm_contiguous` test with the matrix dimensions explicitly set to:

* `M = 768`
* `N = 1536`

The test fails with the following error:

```text
torch.AcceleratorError: CUDA error: an illegal instruction was encountered
```

The error appears to originate from a CUDA kernel execution. Since CUDA errors can be reported asynchronously, the reported stack trace may not point to the actual source of the failure.

For debugging, I also considered using:

```bash
CUDA_LAUNCH_BLOCKING=1
```

and enabling device-side assertions with `TORCH_USE_CUDA_DSA`.

### Question

Is the `M=768, N=1536` shape combination currently supported by the grouped GEMM implementation?

If this shape is expected to be supported, could there be a kernel configuration or shape-related issue causing the illegal instruction?

### Environment

* Test: `test_k_grouped_gemm_contiguous`
* M: `768`
* N: `1536`
* Error: `CUDA error: an illegal instruction was encountered`

Start with the `test_k_grouped_gemm_contiguous` test using M=768 and N=1536, first reproducing it with `CUDA_LAUNCH_BLOCKING=1` as suggested. Determine whether the grouped GEMM implementation supports this shape and, if so, identify the shape or kernel configuration causing the illegal instruction; done means the support status or failure cause is established.

Written by the indexing model from the issue text.