[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