No connection after a while on FileZilla SFTP protocol

Hello,
After a while connected via FileZilla, I have no FTP connection anymore.
FTP server are running in the CWP Panel board.
status:

Dec 09 17:48:14 vps.erotiekfabriek.be systemd[1]: Starting Pure-FTPd FTP server...
Dec 09 17:48:14 vps.erotiekfabriek.be systemd[1]: PID file /var/run/pure-ftpd.pid not readable (yet?) after start.
Dec 09 17:48:14 vps.erotiekfabriek.be pure-ftpd[17314]: (?@?) [DEBUG] Couldn't load the DH parameters file /etc/ssl/private/pure-ftpd-dhparams.pem
Dec 09 17:48:14 vps.erotiekfabriek.be systemd[1]: Started Pure-FTPd FTP server.

I have used the SFTP protocol in FileZilla.
The only thing that not working are the BIND DNS server (failed) and the SSH Sever are in activating position (Yello moon).