martin wrote:

So you are running it in parallel?!? The machine may be overloaded. Did you try increasing Session.Timeout?
https://winscp.net/eng/docs/library_session#timeout

SessionOptions sessionOptions = new SessionOptions
{
    Protocol = Protocol.Sftp,
    HostName = Settings.ftphost,
    UserName = Settings.ftp_username,
    Password = Settings.ftp_password,
    SshHostKeyFingerprint = Settings.SshHostKeyFingerprint,
    PortNumber = int.Parse(Settings.ftp_port)
};
 
using (Session session = new Session())
{
    session.Open(sessionOptions);
 
    if(session.FileExists(remotePath))
    {
        session.RemoveFiles(remotePath);
    }
        
    if (session.Opened == true)
        session.Close();
}

System.TimeoutException: Timeout waiting for WinSCP to respond - WinSCP has not responded in time. There was no output. Response log file C:\abc.tmp was not created. This could indicate lack of write permissions to the log folder or problems starting WinSCP itself.
at WinSCP.Session.CheckForTimeout(String additional)
at WinSCP.Session.Open(SessionOptions sessionOptions)