Reproduce issue https://github.com/mysql-net/MySqlConnector/issues/305

ConsoleApp.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net47</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="dapper" Version="1.50.2" />
    <PackageReference Include="mysqlconnector" Version="0.24.1" />
  </ItemGroup>

  <ItemGroup>
    <Reference Include="Microsoft.CSharp" />
  </ItemGroup>

</Project>

Program.cs

using Dapper;
using MySql.Data.MySqlClient;
using System;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            var builder = new MySqlConnectionStringBuilder
            {
                Server = "localhost",
                UserID = "root",
                Password = "",
                Database = "information_schema",
                MaximumPoolSize = 50,
                ConnectionIdleTimeout = 10,
                AllowUserVariables = false
            };

            var cs = builder.ConnectionString;

            Task.Run(async () =>
            {
                while (true)
                {
                    try
                    {
                        using (var cn = new MySqlConnection(cs))
                        {
                            await cn.OpenAsync();
                            await cn.QueryFirstAsync<int>("SET @test = 1; SELECT @test;");
                        }
                    }
                    catch
                    { }
                }
            });

            using (var cn = new MySqlConnection(cs))
            {
                cn.Open();

                while (true)
                {
                    var o = cn.QueryFirst("select max(time) as MaxSleepTime, count(*) as SleepingConnections from processlist where db = 'information_schema' and command = 'Sleep'");
                    Console.WriteLine($"Sleeping Connections: {(int) o.SleepingConnections}, Max Sleep Time: {(int) o.MaxSleepTime}");
                    Thread.Sleep(1000);
                }
            }
        }
    }
}