"No operations defined in spec!" when using MMLib.SwaggerForOcelot to build combined swagger for Ocelot

This is my ocelot configuration...

{
  "Routes": [
    {
      "UpstreamPathTemplate": "/api/test/{url}",
      "DownstreamPathTemplate": "/api/{url}",
      "DownstreamScheme": "http",
      "DownstreamHostAndPorts": [
        {
          "Host": "test-host",
          "Port": 8080
        }
      ],
      "SwaggerKey": "test"
    }
  ],
  "SwaggerEndPoints": [
    {
      "Key": "test",
      "Config": [
        {
          "Name": "Test API",
          "Version": "v1",
          "Url": "http://test-host:8080/swagger/v1/swagger.json",
        }
      ]
    }
  ]
}

Testing results are as follows...

The downstream endpoint:

• running in a container, without an external port forward
• is alive as an internal call to http://test-host:8080/api/weather-forecast will return an expected result
• is running local swagger at http://test-host:8080/swagger and endpoints are shown and function correctly (json listed below)

The upstream endpoint (via Ocelot):

• running on a different container (with access to downstream) and forwarded to localhost:80
• is routing correctly (as per config) as a call to the external endpoint http://localhost/api/test/weather-forecast is remapping and will correctly return a result from the internal API
• Is providing a central swagger at http://localhost/swagger/ that detects the down stream swagger (shown in the drop down as "Test API", however
• Shows no endpoints! I get the "No operations defined in spec!" provided when the paths object in the spec is empty.

Things I have tried:

• I believe it can see the downstream swagger spec ok because if I add RemoveUnusedComponentsFromScheme: false then it will find and render the models, but still no endpoints; further more intentionally breaking the URL returns an error; so I'm confident the downstream swagger spec is loaded correctly
• If I add TransformByOcelotConfig: false it WILL show the endpoints (further proof the spec if loaded ok), but then the generated url's are wrong; the hostname is correct but the rest of the url uses the internal/downstream path not the re-written external/upstream path
• Bumping package versions up/down to see if its a mismatch (currently Microsoft.AspNetCore.OpenApi 9.0.11, MMLib.SwaggerForOcelot 9.0.0, Swashbuckle.AspNetCore 9.0.6

Downstream swagger doc looks like...

{
  "openapi": "3.0.4",
  "info": {
    "title": "Test API",
    "version": "1.0"
  },
  "paths": {
    "/api/weather-forecast": {
      "get": {
        "tags": ["WeatherForecast"],
        "operationId": "GetWeatherForecast",
        "responses": {
          "200": {
            "description": "OK",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/WeatherForecast"
                  }
                }
              },
              "application/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/WeatherForecast"
                  }
                }
              },
              "text/json": {
                "schema": {
                  "type": "array",
                  "items": {
                    "$ref": "#/components/schemas/WeatherForecast"
                  }
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {
    "schemas": {
      "WeatherForecast": {
        "type": "object",
        "properties": {
          "date": {
            "type": "string",
            "format": "date"
          },
          "temperatureC": {
            "type": "integer",
            "format": "int32"
          },
          "temperatureF": {
            "type": "integer",
            "format": "int32",
            "readOnly": true
          },
          "summary": {
            "type": "string",
            "nullable": true
          }
        },
        "additionalProperties": false
      }
    }
  }
}

Upstream swagger doc looks like...

{
  "openapi": "3.0.4",
  "info": {
    "title": "Test API",
    "version": "1.0"
  },
  "paths": {},
  "components": {
    "schemas": {}
  }
}

What am I missing here?