I just wanted to let you know that you are not the only one experiencing this issue. I have openned a support case with CoreFTP and they are currently trying to reproduce the issue.
Yes, I am also experiencing same issue. The coresftp process is consuming most of the CPU and memory and on the other side the download speed is very slow.
We are using 1.2 version and have around 2-5 users downloading at the same time.
We got in the same situation today as well. It was consuming 50% CPU and was consuming lots of memory.
We had 6 users connected to the sftp server that time. Most of them had action set to List. It was taking an hour to download a 198 MB file within same network.