Comment 2 for bug 1640147

tl;dr: dhclient -6 should be less spam-chatty in the presence of no ipv6 support.

If dhclient logged that as one message, instead of 9 messages, then syslog would compress the output.

The easiest way that I've seen to reproduce this is to boot with ipv6.disable=true on the kernel command line.

Nobuto: do you have ipv6 disabled via the kernel command line? (This is known to cause various issues for a number of daemons.)