In China, all Internet Service Providers must enforce compliance checks, and licenses are required for all HTTP services. Your connection will be aborted during transmission if they are detected before completion. It is said that such checks were deployed at the IDC level, so probably no software-level solution.

In China, all Internet Service Providers must enforce compliance checks, and licenses are required for all HTTP services. Your connection will be aborted during transmission if they are detected before completion. It is said that such checks were deployed at the IDC level, so probably no software-level solution.

But even the two devices under the local router still have this problem

Unable to reproduce. Could you share the code of your testing server?
The snippet I tested can handle hundreds of megs without any problem.

using HttpServer;
using HttpServer.Headers;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System.Net;
using System.Text;

var listener = HttpServer.HttpListener.Create(IPAddress.Parse("0.0.0.0"), 8023);

listener.RequestReceived += OnRequest;
listener.Start(int.MaxValue);
Console.WriteLine("Server started");
Console.ReadLine();

static void OnRequest(object? sender, RequestEventArgs e)
{
    var obj = GenerateResp();
    var str = JsonConvert.SerializeObject(obj, Newtonsoft.Json.Formatting.Indented);
    e.Response.Connection.Type = ConnectionType.Close;
    e.Response.ContentType = new ContentTypeHeader("application/json; charset=utf-8");
    e.Response.Add(new StringHeader("Server", "Test/1.0"));
    var bytes = Encoding.UTF8.GetBytes(str);
    e.Response.Body.Write(bytes, 0, bytes.Length);
    e.Response.Status = HttpStatusCode.OK;
}

static JObject GenerateResp()
{
    var result = new JObject();
    for (var i = 0; i < 100; i++)
    {
        var bytes = new byte[1048576];
        Random.Shared.NextBytes(bytes);
        result.Add("key" + i, Convert.ToBase64String(bytes));
    }
    return result;
}

Update:

Seems Chrome on Android (left) is throttled (Firefox Android, the right one, works perfectly), however, it is not quite related to connection reset.

Here is the plugin code where I'm having trouble

using Rests;
using Terraria;
using TerrariaApi.Server;
using TShockAPI;

namespace TShockRestProblem;

[ApiVersion(2, 1)]
public class TestPlugin : TerrariaPlugin
{
    public override string Name => "Test Plugin";

    public TestPlugin(Main game) : base(game)
    {
    }

    public override void Initialize()
    {
        TShock.RestApi.Register(new RestCommand("/test", TestFunc));
    }

    private object TestFunc(RestRequestArgs args)
    {
        var result = new List<ResultItem>();
        for (var i = 0; i < 40; i++)
        {
            result.Add(ResultItem.CreateRandom());
        }

        return new RestObject
        {
            { "result", result }
        };
    }
}

public class ResultItem
{
    public int Id;
    public string Name;
    public string Description;
    public List<ItemData> Price;
    public List<ItemData> Unlock;

    public static ResultItem CreateRandom()
    {
        return new ResultItem
        {
            Id = RandomNumber(1000),
            Name = RandomString(10),
            Description = RandomString(100),
            Price = RandomItemDataList(RandomNumber(5)),
            Unlock = RandomItemDataList(RandomNumber(5))
        };
    }

    private static int RandomNumber(int max)
    {
        return new Random().Next(max);
    }

    private static string RandomString(int length)
    {
        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789   ";
        return new string(Enumerable.Repeat(chars, length)
            .Select(s => s[new Random().Next(s.Length)]).ToArray());
    }

    private static List<ItemData> RandomItemDataList(int size)
    {
        var list = new List<ItemData>();
        for (var i = 0; i < size; i++)
        {
            list.Add(new ItemData(RandomString(10), RandomNumber(1000), RandomNumber(1000)));
        }

        return list;
    }
}

public class ItemData
{
    public string Name = "";
    public int Id;
    public int Stack = 1;
    public string Cmd = "";

    public ItemData(string name = "", int id = 0, int stack = 1)
    {
        Name = name;
        Id = id;
        Stack = stack;
    }
}

Unable to reproduce. Could you share the code of your testing server? The snippet I tested can handle hundreds of megs without any problem.

using HttpServer;
using HttpServer.Headers;
using Newtonsoft.Json;
using Newtonsoft.Json.Linq;
using System.Net;
using System.Text;

var listener = HttpServer.HttpListener.Create(IPAddress.Parse("0.0.0.0"), 8023);

listener.RequestReceived += OnRequest;
listener.Start(int.MaxValue);
Console.WriteLine("Server started");
Console.ReadLine();

static void OnRequest(object? sender, RequestEventArgs e)
{
    var obj = GenerateResp();
    var str = JsonConvert.SerializeObject(obj, Newtonsoft.Json.Formatting.Indented);
    e.Response.Connection.Type = ConnectionType.Close;
    e.Response.ContentType = new ContentTypeHeader("application/json; charset=utf-8");
    e.Response.Add(new StringHeader("Server", "Test/1.0"));
    var bytes = Encoding.UTF8.GetBytes(str);
    e.Response.Body.Write(bytes, 0, bytes.Length);
    e.Response.Status = HttpStatusCode.OK;
}

static JObject GenerateResp()
{
    var result = new JObject();
    for (var i = 0; i < 100; i++)
    {
        var bytes = new byte[1048576];
        Random.Shared.NextBytes(bytes);
        result.Add("key" + i, Convert.ToBase64String(bytes));
    }
    return result;
}

Update: Seems Chrome on Android (left) is throttled (Firefox Android, the right one, works perfectly), however, it is not quite related to connection reset.

I have no problem running your code, and my code is placed in the previous comment.

Reproduced. It seems that the library is not handling Connection: Close properly.