Intermittent 401001 Error in Azure Translator API Despite Valid Access Token

Hi Azure team,

I’m facing an intermittent issue while integrating the Azure AI Text Translator API with a backend application using a token generated via Azure AD client credentials flow.

🔍 Problem:

The access token is retrieved successfully using an Azure AD App Registration (client credentials flow). The token is valid for 60 minutes and the claims are correct (aud, nbf, exp). However, the Translator API calls behave inconsistently:

• First request often fails with: { "error": {

  "code": "401001",
  
  "message": "The request is not authorized because credentials are missing or invalid."
  

  } }
• The second or third attempt works, fourth, fifth, six failed and 7th works using the same token
• Then a retry works again — all with the same unexpired token
• Token Endpoint Used: https://login.microsoftonline.com/{tenant-id}/oauth2/v2.0/token
• resource: https://cognitiveservices.azure.com, Scope: https://cognitiveservices.azure.com/.default
• Token is passed as: Authorization: Bearer <access_token> Translator API endpoint: https://api.cognitive.microsofttranslator.com/translate?api-version=3.0&from=en&to=de
• Setup:
  • In Azure, I've created the Entra ID application, and generated the secret for that and provide the respective cognitive service user role to the service principle.
  • Authenticate with Microsoft Entra ID: https://learn.microsoft.com/en-us/azure/ai-services/authentication?tabs=powershell#authenticate-with-azure-active-directory
• What We've Tried:
  • Retrying after 401 (sometimes it works)
  • Introducing a 2–3 second delay after token issuance
  • Refreshing the token on 401
  • Using Postman: the same token behaves inconsistently
  • No limits are hit, and the Cognitive Service resource is active
• My Questions:
  1. Why is the Translator API randomly rejecting a valid, unexpired token?
  2. Is this related to regional token propagation across Translator servers?
  3. Are there known caching or delay issues after issuing a new token?
  4. What’s the best-practice recommendation to ensure stable token usage for Translator API across retries?