CWP is main goal is to be a self healing control panel, this means if you have an issue with the FTP connection CWP will try to autoFix it.

How to autoFix your FTP server issue?
- Login to CWP.admin as root
- go to Left Menu --> File Management --> FTP Management
...and that is it.

Simple, if you had any issue once you have opened FTP Management your issue should be resolved.
CWP will auto-check for few well known issues and display you a message about what issue is fixed.

If you still have the same issue then you should contact support.