Login shows "network accounts unavailable" but I can access server once local user logs in
For me, it sometimes takes a moment for the network users to show up.  I found that changing the login window from "List of users" to "Name and password" has made it much better for my users. It seemed that most of the wait was for it to load the list or something.

after making the change, clients will sometimes briefly say that network accounts are unavailable, but its usually very, very brief.