Take a look at this thread How to remove the $ {jboss.node.name} or instance-id in JsessionId? It explains where that value comes from for the session id.

By default, each JSESSIONID will an instance-id appended, as defined by the undertow subsystem.  This value defaults to the "jboss.node.name" system property. The node name itself, will default to the server name, if undefined, which itself defaults to the hostname of the server, if undefined.  It looks like none of these are defined on your system, thus the logic for determining the node name come from here:

wildfly-core/ServerEnvironment.java at 1.0.2.Final · wildfly/wildfly-core · GitHub

Defining any of these precursors will be sufficient to set the node name to something more meaningful (or in your case, less meaningful ).