Multiple [ProducesResponseType] no longer produce multiple schemas since v11.20

[GeorgDangl]

I've noticed that since v11.20, I've had a regression in one of my projects: Using multiple [ProducesResponseType] attributes does no longer produce multiple schemas. While upgrading to 11.20, I've also replaced UseSwaggerUi3(Assembly ...) with UseSwaggerUi3WithApiExplorer(), so this might be related.
The documentation does not mention a difference between the ASP.NET Core built-in attribute and the NSwag.Annotations.SwaggerResponseAttribute, though it works fine with the NSwag one.

To give you a bit of context, this gist contains some more example code: https://gist.github.com/GeorgDangl/acecc279b2cbf7f366a6487eb50d3833

The following controller definition:

[HttpGet("")]
[LightQuery]
[Authorize(Policy = DanglIdentityConstants.Authorization.AUTHENTICATION_CONNECTOR_OR_ADMIN_POLICY_NAME)]
[ProducesResponseType(typeof(PaginationResult<ClientGet>), 200)]
[ProducesResponseType(typeof(ClientGet), 200)]
public IActionResult GetAllClients(string filter = null)
{
    var clientsQuery = _identityServerClientsRepository.GetAllClients()
        .ProjectTo<ClientGet>();
    if (!string.IsNullOrWhiteSpace(filter))
    {
        clientsQuery = clientsQuery.Where(c => c.ClientName.Contains(filter) || c.ClientUri.Contains(filter));
    }
    return Ok(clientsQuery);
}

produces this wrong (shortened) Swagger document:

{
  "operationId": "Clients_GetAllClients",
  "responses": {
    "200": {
      "x-nullable": true,
      "description": "",
      "schema": {
        "$ref": "#/definitions/PaginationResultOfClientGet"
      }
    }
  }
}

When I switch to the NSwag.Annotations.SwaggerResponseAttribute, it is generated correctly:

{
  "operationId": "Clients_GetAllClients",
  "responses": {
    "200": {
      "x-nullable": true,
      "description": "",
      "schema": {},
      "x-expectedSchemas": [
        {
          "description": "",
          "schema": {
            "$ref": "#/definitions/PaginationResultOfClientGet"
          }
        },
        {
          "description": "",
          "schema": {
            "type": "array",
            "items": {
              "$ref": "#/definitions/ClientGet"
            }
          }
        }
      ]
    }
  }
}

I've summed it up in a blog post. The error is not critical, since it's easy to just replace the ASP.NET Core attribute with the one from NSwag, but I didn't find anything in the code / wiki / issues pointing to this (whether it's intentional or already reported).

I'd be happy to help and take a deeper look if you could guide me a bit about where in the code I would start. Thank you for the great work with NSwag!