How to Connect nDisplay using dedicated server

I am developing contents using nDisplay.

In development, we wanted to build a multiplayer environment using Dedicated Server,
so we tried to connect with the server using the Open Level BP(Open IP Address) feature through Cluster Event.

In some cases, the connection is good, and in some cases, the connection is not possible.

The nDisplay Log file displays the following message.

Does anyone know how to solve this problem?