I've had similar issues. Google for NetworkManager-wait-online.service and
you will probably find something to help. This is a service that uses
"nm-online" to wait for NetworkManager to report itself ready before
exiting. I can't remember all the details of making use of this, but one of
my systems needed it to avoid this sort of issue, where something would try
to start before all the network interfaces were actually up.
--Greg