Network Browsing

Working in a Windows Network Environment with an AD server in 15 locations. When browsing entire network, some servers do not always show up on the browse list. Some times they are present, and some times they are not. I can UNC path (\\servername) to a server that does not show up and it comes up fine.

Any ideas what might cause this and whether there is a configuration change that may resolve the issue?

Thanks.