Open Directory issues - OS X 10.11.6 - Server 5.1.7

I am working with a business that has an all Mac network and a few servers. There is one master OD server and a few replicas. Some time ago, I demoted an old Mac server to put a new Mac Mini server in its place. The process of getting the new server setup was challenging, but, it finally did work (mostly).

One of the things I am still trying to figure out is, why certain users can login to the computers but others cannot. If a user that cannot login on one, moves to another computer, they sometimes can login. It's difficult to know why this is the case and I am looking for some input from the community if possible.

Another thing that raises an eyebrow is all the references I see in Directory Utility to the old Master, where I believe it should be the new Master.

Does anyone have any thoughts?

Thanks,

Nate