Updating phpseclib
The version of phpseclib that comes with Magento 1 is super old. If you have issues with SFTP exports you can try updating phpseclib manually.
- Log in via FTP
- Go into root Magento directory
- Go into the "lib" folder
- Create a backup of the "phpseclib" folder. Then rename the folder to "phpseclib2".
- Find a working / recent version of phpseclib compatible with your Magento installation.
- Test everything and make sure the export as well as the store in general works.