[CentOS] CentOS 7, NetworkMangler, and ipv6

We've started having a problem with a CentOS 7 server. It looses its IPv6
address, if I understand this issue correctly. We can get in, if we do ssh
-4, though.

In the logs, I'm seeing this about twice an hour:
<warn>  (pid 98466) unhandled DHCP event for interface ens3f0

Now, in googling, I get very few hits putting quotes around "unhanded dhcp
exception" - in fact, the only one I found that seemed to talk about it
was from someone's slackware box, where there was some sort of
configuration, perhaps similar to ifcfg-<if>, and they were telling that
person to remove it, because it conflicted with what Networkmanager was
trying to do, leaving it in a confused state.

Any thoughts?

       mark