Gemini Batch API jobs with gemini-3.1-flash-preview do not reach SUCCEEDED after 24+ hours

### Description

Since approximately **2026-09-15**, Gemini Developer API (AI Studio API) batch jobs using `gemini-3.1-flash-preview` have not transitioned to `JOB_STATE_SUCCEEDED`, even after more than 24 hours.

The jobs are created successfully, but polling them with `client.batches.get()` continues to return a non-terminal state without a useful error. This started suddenly in a production catalog-processing pipeline; the same integration had previously completed batch jobs normally.

This appears similar to past incidents reported in:
- #1482
- #2221

Both previous issues are closed, so I am reporting this as a possible recurrence.

### Environment

- API: Gemini Developer API / Google AI Studio API (**not Vertex AI**)
- Language: Python
- SDK: `google-genai==1.60.0`
- Model: `models/gemini-3.1-flash-preview`
- Input: JSONL file uploaded through the Files API
- First observed: 2026-09-15

### Minimal flow

```python
import os
from google import genai

client = genai.Client(api_key=os.environ["GEMINI_API_KEY"])

uploaded_file = client.files.upload(
file="input.jsonl",
config={"mime_type": "jsonl"},
)

job = client.batches.create(
model="models/gemini-3.1-flash-preview",
src=uploaded_file.name,
config={"display_name": "batch-test"},
)

# Still does not reach JOB_STATE_SUCCEEDED after 24+ hours
current_job = client.batches.get(name=job.name)
print(current_job.state)
```

### Expected behavior

The batch job should complete within the documented processing window, or fail with an actionable error.

### Actual behavior

The job remains in a non-terminal state for more than 24 hours and does not produce output or an actionable error.

### Additional information

We can provide affected batch job names privately to maintainers if needed, but have omitted account/project identifiers and job IDs from this public report.

Could you confirm whether there is a current service-side incident or elevated queueing for Gemini Developer API batch jobs using `gemini-3.1-flash-preview`?