ERROR: FTP server reply: 530 Maximum number of tries exceeded

Hi for a few days already all of my wordpress/backwpup installations from one specific shared hosted webspace exit with a

[25-Nov-2016 12:14:03] FTP server reply: 331 Password required for xy.
[25-Nov-2016 12:14:03] FTP client command: PASS *******
[25-Nov-2016 12:14:03] ERROR: FTP server reply: 530 Maximum number of tries exceeded.

these backups go to a FTP Server on a Synology NAS via DDNS, which is well reached by wordpress/backwpup installs on a different shared hosted webspace and via ftp clients/console.

Backups to other FTP servers work fine.

Ideas? Thanks!