Did you also try a fresh CSF/LFD installation on a fresh Debian 9.4 installation and build from there? I have several Debian 9.4 servers running (with postfix) and they are all working fine.
What are the exact errors in the log? It might be that CSF/LFD are not able to pick it up and you need to configure a custom regex. viewtopic.php?f=6&t=7517
What did you change? Did you not make a backup? Did your check your settings in /etc/csf/csf.conf? At the top you can open up IPv4 and IPv6 ports and enable ICMP for pings.
Thank you for your reply. I wasn't clear. I can ping with IPv4 to www.google.com etc. but not to a server with CSF / LFD installed. root@backup01:~# cat /etc/debian_version 9.3 root@backup01:~# grep "ICMP_.* =" /etc/csf/csf.conf ICMP_IN = "1" ICMP_IN_RATE = "1/s" ICMP_O...