Cannot remove specific contact from Find My

This is the second time I'm coming back to this problem as since it occurred it's still not addressed.

There is a specific contact that cannot be deleted from Find My (Friends).

I want to clarify from the beginning that this is neither a network issue nor a device issue since I have been trying to delete this specific person for 2 years almost, and since then I've changed many devices. Furthermore I work on software engineering for more than 10 years, consisting me capable to explore the issue throughout.

A copy of the request header and the response body I debugged is following.

It's a 500 error for some reason, but only when deleting this specific contact.

  "commandResponse": {
    "statusCode": "500"
  },

(For obvious reasons I masked the sensitive fields)

POST /fmipservice/friends/<masked>/<masked>/removeFollowing HTTP/1.1

{
  "serverContext": {
    "minCallbackIntervalInMS": 1000,
    "res": null,
    "clientId": "<masked>",
    "showAirDropImportViewOniCloudAlert": true,
    "authToken": "<masked>",
    "maxCallbackIntervalInMS": 5000,
    "prsId": <masked>,
    "callbackTimeoutIntervalInMS": 0,
    "heartbeatIntervalInSec": 543600,
    "transientDataContext": {
      "0": <masked>,
      "1": 0,
      "2": <masked>,
      "3": <masked>,
      "4": <masked>
    },
    "sendMyLocation": true,
    "notificationToken": null,
    "iterationNumber": 15
  },
  "modelVersion": "1",
  "fetchStatus": "200",
  "dataContext": {
    "0": <masked>,
    "1": <masked>,
    "2": <masked>,
    "5": <masked>,
    "6": <masked>,
    "8": <masked>,
    "9": "<masked>",
    "10": <masked>,
    "11": <masked>,
    "12": <masked>,
    "13": <masked>,
    "18": <masked>,
    "19": <masked>,
    "20": <masked>,
    "21": <masked>,
    "22": <masked>
  },
  "commandResponse": {
    "statusCode": "500"
  },
  "locations": [
    {
      "locationStatus": null,
      "location": null,
      "id": "<masked>",
      "status": null
    }
  ],
  "locateInProgress": [
    {
      "id": "<masked>",
      "status": "none"
    },
    {
      "id": "<masked>",
      "status": "none"
    }
  ]
}