If you are running a cluster of Lightstreamer Server behind a Load Balancer, you have to ensure client stickiness, at least at session level.
The general discussion can be found in the Clustering.pdf document.
With reference to that document, if you opt for leveraging "Load Balancer stickiness", this may require that the client can manage HTTP cookies in the appropriate way, that is, according with RFC 2965 or 6265, as browsers do.

This is not the default for java client applications based on Lightstreamer Java Client Library, which leans on the standard JDK support for HTTP management.
However, since Java 6, you can enable the correct support of client cookies by issuing the following JVM-wide setting before using Lightstreamer library code: