Weird problem when comparing the answers from chat playground and answer from api

I'm running into a weird issue with Azure AI Foundry (gpt-4o-mini) and need help.

I'm building a chatbot that classifies each user message into:

1. follow-up to previous message
2. repeat of an earlier message
3. brand-new query

The classification logic works perfectly in the Azure AI Foundry Chat Playground.
But when I use the exact same prompt in Python via:

• AzureChatOpenAI() (LangChain)
• or the official Azure OpenAI code from "View Code" (client.chat.completions.create())

…I get totally different and often wrong results.

I’ve already verified:

• same deployment name (gpt-4o-mini)
• same temperature / top_p / max_tokens
• same system and user messages
• even tried copy-pasting the full system prompt from the Playground

But the API version still behaves very differently.

It feels like Azure AI Foundry’s Chat Playground is using some kind of hidden system prompt, invisible scaffolding, or extra formatting that is NOT shown in the UI and NOT included in the “View Code” snippet. The Playground output is consistently more accurate than the raw API call.

Question:
Does the Chat Playground apply hidden instructions or pre-processing that we can’t see?
And is there any way to:

• view those hidden prompts, or
• replicate Playground behavior exactly through the API or LangChain?

If anyone has run into this or knows how to get identical behavior outside the Playground, I’d really appreciate the help.