webapi NetCore json 仅返回每个嵌套列表的最后一个元素

Question

The problem: I am trying to match a given signature of an API to replace the underlaying implementation.

I created the proyect as dotnet new webapi and duplicated the controller.

My new controller works when posting a simple object (first method), but second fails to populate a nested list: It adds only the last element of a nested item.

Using swagger, I post this json:

{
  "fileContent": "the file content",
  "metadata": [
    {
      "name": "alfa",      "value": ["aa"],
      "name": "beta",      "value": ["bb"],
      "name": "gama",      "value": ["gg"]
    },
{
      "name": "delta",      "value": ["dd"],
      "name": "epsilon",      "value": ["ee"],
      "name": "omega",      "value": ["oo"]
    }
  ]
}

I return the same object, but I just get:

{
  "fileContent": "the file content",
  "metadata": [
    {
      "name": "gama",
      "value": [
        "gg"
      ]
    },
    {
      "name": "omega",
      "value": [
        "oo"
      ]
    }
  ]
}

The full webapi controller:

[ApiController]
[Route("[controller]")]
public class CrappyController : ControllerBase
{  
    private readonly ILogger<CrappyController> _logger;

    public CrappyController(ILogger<CrappyController> logger)
    {
        _logger = logger;
    }

    [HttpPost(Name = "v1/CreateAttachment")]
    public CreateAttachmentV1 Create(CreateAttachmentV1 createAttachment)
    {
        _logger.LogInformation("CreateAttachment.V1");
            
        return createAttachment;
        // .ToArray();
    }


    [HttpPatch(Name = "v1/CreateAttachment")]
    public UpdateAttachmentV1 UpdateAttachment(UpdateAttachmentV1 data)
    {
        _logger.LogInformation("UpdateAttachment.V1");
            
        return data; // please notice I return the same object for debugging
    }
}

And the method classes

    public struct NameValueList<TKey, TArray>
    {
        public TKey Name { get; set; }
        public string[]? Value { get; set; }
    }

    public class UpdateAttachmentV1
    {
        public string? FileContent { get; set; }
        
        public List<NameValueList<string, string>>? Metadata { get; set; }
    }

    public class CreateAttachmentV1
    {
        public string FileCategory { get; set; }

        public string FileName { get; set; }
    }

I am puzzled. It compiles, signature matches on swagger,but jumps over all but last element on each Metadata array.