The "Modified" (timestamp) column for all file objects shows as "Unknown" for Couchdrop SFTP server. I've confirmed I do see modified timestamps as expected on an sftp connection with different client connected to same server so the problem may be limited to when using Couchdrop.
I can confirm the issue is the same as when connected to Couchdrop FTP server instead of SFTP.
I have just tested this with an account and can reproduce the problem. The server does not send the required attribute flags as defined in valid-attribute-flags. Not sure yet how OpenSSH sftp manages to display a meaningful value.