I noticed that when modifying user records in Server.app 5.x, like adding a user to a group, the file server did not get the update instantly but after some time (hours).
this was mostly really true for smb connections but afp connexions are too impacted.
the command is really simple, simply wipe the OpenDirectory cache on the slave server and voila.
sudo odutil reset cache
Then try to reconnect with the modified user, and there you go, you’ve forced a refresh.
Tested on 10.10.3 Os X Server (OD master) and 10.10.5 Os X Server (File sharing)