For some reason when a Mac mini was updated to Mac OS X El Capitan, shared folders made the connection, but new files listed on the host were not being shared with the client Mac running Mac OS X 10.8.5. File in the folder might show at the initial connection, but any files added might not show in the display on the client Mac.
HERE IS THE FIX ...
Go to system preference on the host Mac
Go to Sharing on the host mac
Make Sure File Sharing is Checked (left)
Click the Options Button
Check "Share files and folders using AFP" to use the legacy file sharing protocol for Apple Macs. If there are no Windows machines on your network, turn off SMB (Windows).
You may have to login to the host again. Also, if had an alias in the sidebar, you may have to remove the old alias from the sidebar, and drag in a new alias for the connection.
The reason the change is necessary is caused by the fact that The Apple Filing Protocol (AFP), which has been Apple's default networking protocol in the classic Mac OS as well as in OS X, has been replaced with SMB2.
Server Message Block (SMB) is a file transfer protocol that has been the main networking protocol for Windows-based systems. Having different default protocols has made the use of both Windows and Mac systems on the same network frustrating, since until Apple introduced native SMB support in OS X, users had to rely on third-party SMB support for sharing files with Windows systems.
The Server Message Block (SMB) Protocol is a network file sharing protocol, and as implemented in Microsoft Windows is known as Microsoft SMB Protocol. The set of message packets that defines a particular version of the protocol is called a dialect. The Common Internet File System (CIFS) Protocol is a dialect of SMB.