EOSCore 1.9.1.7 and onwards has limited LAN support, the EOS SDK does not have the ability to login to EOS accounts when offline so this functionality can not be used on non-internet connected LAN connections.
To use LAN functionality you will first have to authenticate with EOS as usual, see the Authentication documentation.
Make sure to check the “Is lan Match” checkbox when creating the session, another important step is to append bIsLanMatch when opening the game map, this will force the NetDriver to use an IP connection instead of the EOS connect string.