The timeout should arise only in case the client didn't receive any data from the server for specified time. Directory listing is typically performed using multiple
SSH_FXP_READDIR requests. Even for very large directories the timeout should not arise.
It seems that the server got stucked for some reason or it tries to send all listed items at once.
Can you please create communication log and send it to firstname.lastname@example.org for analysis. Based on the finding, we can provide you a solution.
The log can be created like this:
dSftp.LogWriter = new Rebex.FileLogWriter(@"C:\data\sftp.log", Rebex.LogLevel.Info);
SftpItemCollection list = dSftp.GetList(strServerPath + "//" + "*." + extension);