Comment # 11 on bug 1212627 from Jonathan Kang

In your setup, NetworkManager logs "startup complete" when ipv4 succeeds, and
this triggers NetworkManager-wait-online to quit. But at that moment,
NetworkManager is still at the process of setting manual ipv6 address. This is
caused by the "ipv6.may-fail" property defaulting to TRUE. So when dhcp4
succeeded, NetworkManager thought it's time to finish the startup.

Can you try setting "ipv6.may-fail" to FALSE and see if this makes any
difference?

> nmcli connection modify Wired\ Connection\ 1 ipv6.may-fail no