Thanks for the reply!
It was actually the FXP_READ issue again where only 1 Max Queued Request can be handled.
Setting it to 1 with SSHFTPClient.setMaxQueuedReadRequests() did the trick for this customer we interface with!
Very cool, but, good to know that speed also can be throttled and not a good idea to pursue and getting to the bottom of the underlying problem is best.
Thanks!
Jan