If you just set it up, it takes time to replicate between AD and the other Unity servers. Give it an hour or so. But if it still does not work, you can remove the setup in the SA page, wait an hour, then set it back up again wait an hour. (or however long).
if you have a Unity server that was rebuilt (crashed or something) the Location ID in Unity and AD is mismatched or needs to be cleaned out manually and recreated. I had a problem with replication in AD and Unity because it turns out, the Unity server was rebuilt some time ago.
