(Rebex.FTP/SSL) Very slow download speed from within docker container.

Hello!

I have a very interesting issue here.

Shortly:
We have a simple .NET Core 2.1 application that downloads stuff from FTP server within same network (10 GBit network) and achieves maximum speed of ~16 Mbps when launched within docker container.

Same app reaches 200 Mbps when started from outside docker.

There is nothing special, here is our test app code:

var client = new Ftp();
Rebex.Licensing.Key = "...";

client.ValidatingCertificate += (sender, args) => {
 args.Accept();
};

var sslMode = SslMode.Explicit;
var ftpUri = new Uri("ftp://local-network-server/");

// Connect securely using explicit or implicit SSL.
if (ftpUri.Port > 0)
    client.Connect(ftpUri.Host, ftpUri.Port, sslMode);
else
    client.Connect(ftpUri.Host, sslMode);

client.SecureTransfers = true;
client.Timeout = (int) TimeSpan.FromMinutes(5).TotalMilliseconds;
client.Settings.KeepAliveDuringTransfer = true;
client.Settings.KeepAliveDuringTransferInterval = 60;
client.Settings.PauseBeforeUploadClose = true;
client.Settings.UseLargeBuffers = true;
client.UploadBufferLength = 256 * 1024; // 256 KB
client.Settings.SslReuseSessions = true;

// Connection is protected now, we can log in safely.
client.Login("user", "pass");

client.DownloadAsync("/path/to/folder", Directory.GetCurrentDirectory(), TraversalMode.Recursive, TransferMethod.Copy, ActionOnExistingFiles.OverwriteAll).Wait();

client.Disconnect();

Here is our Dockerfile:

FROM microsoft/dotnet:2.2-runtime

# Set current work dir.
WORKDIR /app

# Copy app build.
ADD ./bin/Debug/netcoreapp2.1/publish/ ./

# Start app.
ENTRYPOINT ["dotnet", "Expsz.dll"]

Rebex.FTP Nuget - 4.0.6930
Rebex.Common Nuget - 2.5.6930
Rebex.Networking Nuget - 3.5.6930

IMPORTANT
As an alternative I tried FluentFTP lib from within container, it doesnt have such issues and is able to achieve good speeds. Also fetching stuff via curl/wget also works good.

Any ideas? Might it be due to docker base image? Does Rebex.Ftp rely on some OS things?

Anything more I can provide to make things clear?
Any help is appreciated. Thanks!