I just did try to upgrade to version 1.4.1 (from latest 1.3.x) and have some error messages during upgrading (see file attachment). And maybe the output below gives you a hint what is going wrong (seems something with IPv6 issue). I alread did search in google and i-mscp forum but I´m a little bit afraid of doing some things that I really don´t understand fully and maybe it is getting more worse than right now...
My Server runs on Debian 8.7 Jessie
root@srv /usr/local/src/imscp-1.4.1/engine/PerlLib # systemctl status imscp_traffic.service
● imscp_traffic.service - i-MSCP traffic logger
Loaded: loaded (/etc/systemd/system/imscp_traffic.service; enabled)
Active: failed (Result: exit-code) since Fri 2017-03-31 08:41:51 CEST; 4min 17s ago
Process: 3193 ExecStop=/usr/bin/perl /var/www/imscp/engine/tools/imscp-net-traffic-logger stop (code=exited, status=0/SUCCESS)
Process: 3208 ExecStart=/usr/bin/perl /var/www/imscp/engine/tools/imscp-net-traffic-logger start (code=exited, status=3)
Main PID: 3208 (code=exited, status=3)
Mar 31 08:41:51 srv systemd: Starting i-MSCP traffic logger...
Mar 31 08:41:51 srv perl: [ERROR] main::start: modprobe: ERROR: could not insert 'ip6_tables': Unknown symbol in module, or unknown parameter (see dmesg)
Mar 31 08:41:51 srv perl: ip6tables v1.4.21: can't initialize ip6tables table `filter': Table does not exist (do you need to insmod?)
Mar 31 08:41:51 srv perl: Perhaps ip6tables or your kernel needs to be upgraded.
Mar 31 08:41:51 srv systemd: imscp_traffic.service: main process exited, code=exited, status=3/NOTIMPLEMENTED
Mar 31 08:41:51 srv systemd: Failed to start i-MSCP traffic logger.
Mar 31 08:41:51 srv systemd: Unit imscp_traffic.service entered failed state.