Elastic Beanstalk isn't designed for FTP because the point of it is that it can create and dump instances whenever it needs and when an instance is dumped everything in it is lost. If you need to FTP then its better to use a EC2 instance
Feel free to comment if you can add help to this page or point out issues and solutions you have found. I do not provide support on this site, if you need help with a problem head over to stack overflow.