suggested-question API request always return empty content

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### Dify version

1.17.0

### Cloud or Self Hosted

Cloud

### Steps to reproduce

suggested-question API request always return empty content, its setting is keeping in default

### ✔️ Expected Behavior

return three questions

### ❌ Actual Behavior

the content AI answers is pretty rich, but sugestion-question always return empty content

Start with the suggested-question API request and trace how the AI response is converted into suggested questions. Reproduce the request using the reported default settings, then verify that the response contains three question entries rather than empty content.

Written by the indexing model from the issue text.