It's most likely caused by a known bug in Cerberus SFTP server:
https://winscp.net/forum/viewtopic.php?t=15504

WinSCP 5.7.5 with a workaround will be released later today or tomorrow.
https://winscp.net/tracker/1338

On a connection to a remote sftp server - in this case cerberus ftp - remote file listing does not contain any directory entries, only files are listed. Accessing the directories by entering the diretory name is possible. Winscp versions until version 5.5.6 are able to list files and directories on the remote server. Other clients are also able to list files and directories (tested with: Filezilla [latest version] and openssh sftp [OpenSSH_6.7p1]). Sorry but i can not provide more information at the moment.

Versions affected: 5.6.x - 5.7.4
OS: Windows 7 Professional
OS Architecture: arbitrary
OS Updates: arbitrary
Current solution: downgrade to version 5.5.6