Unfortunately I can't get you neither the log files, nor the output of the command. I'm not allowed to do it. But I can tell you that the output of the command is all our equipment connected to the server, both the reserved equipment and the ones using DHCP. But there is no duplication now.
Also, in the messages log, I was able to find 2 lines that were causing the issues. A very simple form of the lines are:
Nov 30 08:04:11 firewall dnsmasq-dhcp: DHCPACK(enp2s10) X.Y.Z.28 17:6a:54:XX:X:XX old-workstation
Nov 30 08:24:00 firewall dnsmasq-dhcp: DHCPACK(enp2s10) X.Y.Z.28 28:dd:bd:XX:X:XX new-laptop
As you can see, the old laptop booted up and since it has a reserve IP, it received it (X.Y.Z.28). Later a new PC was booting with DHCP settings and it received the exact same IP. And this was the confusion all about.