Microsoft Graph API returns 502 Bad Gateway (UnknownError) when calling List members of a chat

Description:

I am encountering a persistent 502 Bad Gateway error with the UnknownError code when attempting to list members of a specific chat via the Microsoft Graph API v1.0. This issue occurs even though the chat ID is valid and the authorization token has the necessary permissions.

API Endpoint:

GET /v1.0/chats/{chat-id}/members

Steps to Reproduce:

1. Obtain a valid access token with Chat.Read or Chat.ReadWrite permissions.

2. Call the endpoint for a meeting chat:

https://graph.microsoft.com/v1.0/chats/19:meeting_NmU5Yjk3NTAtYTk2ZS00Yzg0LWEyYmQtZTJhMjI4NmJjZmRh@thread.v2/members

3. The API returns a 502 Bad Gateway response.

Debug Information (Request Details):

* Date: 2026-02-06 06:17:55 (GMT)

* Request ID: be906f9e-2108-4722-91b8-ecee8bfb41f0

* Client Request ID: be906f9e-2108-4722-91b8-ecee8bfb41f0

* DataCenter: Germany West Central

* X-ms-ags-diagnostic: {"ServerInfo":{"DataCenter":"Germany West Central","Slice":"E","Ring":"4","ScaleUnit":"001","RoleInstance":"FR2PEPF0000118F"}}

Raw Response Body:

{

"error": {

"code": "UnknownError",

"message": "Bad Gateway",

"innerError": {

"date": "2026-02-06T06:17:55",

"request-id": "be906f9e-2108-4722-91b8-ecee8bfb41f0",

"client-request-id": "be906f9e-2108-4722-91b8-ecee8bfb41f0"

}

}

}

Additional Context:

The connection is established successfully via TLS 1.3, but the upstream server seems to be failing. This happens specifically with meeting-related chat threads. Could you please investigate if there is a service degradation or a specific issue with this chat object in the Germany West Central region?