SftpClient UploadFile throws SocketException: 'An existing connection was forcibly closed by the remote host'

This exception has been thrown when VPN client is connected. Same code works fine if VPN is switch off.

StackTrace:

at System.Net.Sockets.Socket.Send(Byte[] buffer, Int32 offset, Int32 size, SocketFlags socketFlags)
at Renci.SshNet.Abstractions.SocketAbstraction.Send(Socket socket, Byte[] data, Int32 offset, Int32 size)
at Renci.SshNet.Session.SendPacket(Byte[] packet, Int32 offset, Int32 length)
at Renci.SshNet.Session.SendMessage(Message message)
at Renci.SshNet.Session.Renci.SshNet.ISession.SendMessage(Message message)
at Renci.SshNet.Channels.Channel.SendData(Byte[] data, Int32 offset, Int32 size)
at Renci.SshNet.Channels.Channel.SendData(Byte[] data)
at Renci.SshNet.SubsystemSession.SendData(Byte[] data)
at Renci.SshNet.Sftp.SftpSession.SendRequest(SftpRequest request)
at Renci.SshNet.Sftp.SftpSession.RequestWrite(Byte[] handle, UInt64 serverOffset, Byte[] data, Int32 offset, Int32 length, AutoResetEvent wait, Action1 writeCompleted) at Renci.SshNet.SftpClient.InternalUploadFile(Stream input, String path, Flags flags, SftpUploadAsyncResult asyncResult, Action1 uploadCallback)
at Renci.SshNet.SftpClient.UploadFile(Stream input, String path, Boolean canOverride, Action`1 uploadCallback)

Start by reproducing SftpClient.UploadFile with the reported VPN condition, then trace the failure through SftpClient.InternalUploadFile, SftpSession.RequestWrite, Session.SendPacket, and SocketAbstraction.Send. Compare behavior with and without the VPN and determine whether the issue can be isolated to a reproducible library or environment condition; done means documenting the cause and an actionable fix or limitation.