Updated by info missing

When requesting a device, sometimes (yes I know it sounds weird), the updated_by property is missing, although the device was updated.

I'm requesting a device like so:

GET http://rz-vm64.gfz-potsdam.de:3001/backend/api/v1/devices/3?include=created_by.contact,updated_by.contact

This is the response that I got:

{
  "data":{
    "type":"device",
    "attributes":{
      "status_name":"",
      "manufacturer_name":"",
      "is_public":false,
      "status_uri":"",
      "created_by_id":"2", // <-- this is fine, but where is "updated_by_id"?
      "manufacturer_uri":"",
      "description":"dfdfdf",
      "inventory_number":"",
      "device_type_uri":"http://rz-vm64.gfz-potsdam.de/cv/api/v1/equipmenttypes/49/",
      "persistent_identifier":null,
      "long_name":"",
      "model":"",
      "short_name":"Test Device",
      "is_internal":true,
      "is_private":false,
      "website":"",
      "dual_use":false,
      "group_ids":[
        "1316",
        "1315"
      ],
      "created_at":"2022-03-28T13:13:58.963984",
      "updated_at":"2022-03-31T09:09:43.703704",
      "device_type_name":"Altimeter",
      "serial_number":""
    },
    "relationships":{
      "updated_by":{
        "links":{
          "self":"/backend/api/v1/devices/3/relationships/updated-user"
        },
        "data":null // <-- huh, why it is null?
      },
      "device_attachments":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/device-attachments"
        },
        "data":[
          
        ]
      },
      "device_mount_actions":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/device-mount-actions"
        },
        "data":[
          
        ]
      },
      "device_properties":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/device-properties"
        },
        "data":[
          
        ]
      },
      "device_unmount_actions":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/device-unmount-actions"
        },
        "data":[
          
        ]
      },
      "customfields":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/customfields"
        },
        "data":[
          
        ]
      },
      "device_software_update_actions":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/device-software-update-actions"
        },
        "data":[
          
        ]
      },
      "events":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/events"
        },
        "data":[
          
        ]
      },
      "contacts":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/contacts"
        },
        "data":[
          {
            "type":"contact",
            "id":"2"
          }
        ]
      },
      "device_calibration_actions":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/device-calibration-actions"
        },
        "data":[
          
        ]
      },
      "configuration_device":{
        "links":{
          "self":"/backend/api/v1/devices/3/relationships/configuration-device"
        },
        "data":{
          "type":"configuration_device",
          "id":"[]"
        }
      },
      "generic_device_actions":{
        "links":{
          "related":"/backend/api/v1/devices/3/relationships/generic-device-actions"
        },
        "data":[
          
        ]
      },
      "created_by":{
        "links":{
          "self":"/backend/api/v1/devices/3/relationships/created-user",
          "related":"/backend/api/v1/users/2"
        },
        "data":{ // <-- yes I want this!
          "type":"user",
          "id":"2"
        }
      }
    },
    "id":"3",
    "links":{
      "self":"/backend/api/v1/devices/3"
    }
  },
  "links":{
    "self":"/backend/api/v1/devices/3"
  },
  "included":[
    {
      "type":"user",
      "attributes":{
        "subject":"mhanisch@gfz-potsdam.de"
      },
      "relationships":{
        "contact":{
          "links":{
            "self":"/backend/api/v1/users/2/relationships/contact",
            "related":"/backend/api/v1/contacts/2"
          },
          "data":{
            "type":"contact",
            "id":"2"
          }
        }
      },
      "id":"2",
      "links":{
        "self":"/backend/api/v1/users/2"
      }
    },
    {
      "type":"contact",
      "attributes":{
        "email":"marc.hanisch@gfz-potsdam.de",
        "active":true,
        "given_name":"Marc",
        "family_name":"Hanisch",
        "website":"dfdf"
      },
      "relationships":{
        "user":{
          "links":{
            "self":"/backend/api/v1/contacts/2/relationships/user"
          },
          "data":{
            "type":"user",
            "id":"2"
          }
        },
        //...
        "devices":{
          "links":{
            "related":"/backend/api/v1/contacts/2/relationships/devices"
          },
          "data":[
            {
              "type":"device",
              "id":"3"
            }
          ]
        }
      },
      "id":"2",
      "links":{
        "self":"/backend/api/v1/contacts/2"
      }
    }
  ],
  "jsonapi":{
    "version":"1.0"
  }
}

My assumption is, that the updated_by property is not set when the user is the same as the one who created the device?