Can't delete an ExternalGroup using the Graph API

I have an application that syncs groups from a 3rd party app into Graph API using an ExternalConnection and by recreating groups when memberships change - i.e. a delete followed by a create. Most groups work as expected. However some groups end up in an invalid state and can't be deleted. For example

DELETE: https://graph.microsoft.com/v1.0/external/connections/MyTestConnection/groups/10C5L10R6/

NOTE: Exact same response using the beta endpoint too

Response: 409 Conflict

{
  "error": {
    "code": "NameAlreadyExists",
    "message": "The specified resource name already exists",
    "innerError": {
      "code": "UnclassifiedConflict",
      "message": "Conflict occurred but could not be classified into a known category.",
      "date": "2026-04-08T00:24:08",
      "request-id": "dbbbee76-1998-479b-b2d1-df51c0287f62",
      "client-request-id": "dbbbee76-1998-479b-b2d1-df51c0287f62"
    }
  }
}

Additional troubleshooting

Fetching the ExternalGroup

Checking to see if it does actually exist

GET: https://graph.microsoft.com/v1.0/external/connections/MyTestConnection/groups/10C5L10R6/

Response: 200 OK

{
  "@odata.context": "https://graph.microsoft.com/v1.0/$metadata#external/connections('MyTestConnection')/groups/$entity",
  "id": "10C5L10R6",
  "displayName": null,
  "description": null
}

That seems OK.

Updating the ExternalGroup

Seeing if I can at least make other changes to the ExternalGroup

PATCH: https://graph.microsoft.com/v1.0/external/connections/MyTestConnection/groups/10C5L10R6/

BODY: { "displayName": "Why can't I delete you" }

Response: 409 Conflict

{
  "error": {
    "code": "NameAlreadyExists",
    "message": "The specified resource name already exists",
    "innerError": {
      "code": "UnclassifiedConflict",
      "message": "Conflict occurred but could not be classified into a known category.",
      "date": "2026-04-08T01:20:27",
      "request-id": "639be94f-1d2e-4b10-a8a4-bc284e3fe345",
      "client-request-id": "639be94f-1d2e-4b10-a8a4-bc284e3fe345"
    }
  }
}

Trying to Create the same ExternalGroup

Trying a Create, just to see if that provides more info :

POST: https://graph.microsoft.com/v1.0/external/connections/MyTestConnection/groups

BODY: {"id": "10C5L10R6" }

Response: 500 Internal Server Error

{
  "error": {
    "code": "GeneralException",
    "message": "There was an internal server error while processing the request.",
    "innerError": {
      "date": "2026-04-08T01:14:09",
      "request-id": "dcbb3ede-5df6-49ed-a835-9fb9ffecb596",
      "client-request-id": "dcbb3ede-5df6-49ed-a835-9fb9ffecb596"
    }
  }
}

The expected Create response if the group existed would be:

Response: 409 Conflict

{
  "error": {
    "code": "NameAlreadyExists",
    "message": "The specified resource name already exists",
    "innerError": {
      "date": "2026-04-08T01:15:49",
      "request-id": "535c4939-67f5-4891-9486-7feadb502f79",
      "client-request-id": "535c4939-67f5-4891-9486-7feadb502f79"
    }
  }
}

Any assistance or information would be greatly appreciated.