not artwork (poster, etc) when using ftp

hello friends I am having an issue where kodi wont load local artwork (logo, poster, etc) when using my ftp server, i have test it with smb and sftp and it is working with those protocols, however sftp seen to be slower thank ftp so i can not use it, i also test kodi 18 but same issue, if anybody know how to fix it i will appreciate it if you can help me. thank you.