The issue EAPSUP-662 revealed some restrictions on the use of the EJB client protocol EJB/HTTP and consequently some missing documentation.
For the record,here are the docs for EAP 7.4:

• Release Notes
• JBoss Enterprise Application Platform Expansion Pack
  • RedHat JBoss EAP XP 3.0.0 Release Notes
  • JBoss EAP XP Upgrade and Migration Guide
  • Using Microprofile with JBoss EAP XP 3.0.0
  • JBoss EAP XP 3.0.0 Quickstarts
• Deployment
  • JBoss EAP Quickstarts
  • Introduction to JBoss EAP
  • Getting Started Guide
  • Getting Started with JBoss EAP for OpenShift Online
  • Getting Started with JBoss EAP for OpenShift Container Platform
• Installation and Upgrade
  • Installation Guide
  • Migration Guide
  • Patching and Upgrading Guide
  • Using the JBoss Server Migration Tool
• Development
  • Development Guide
  • Developing Web Services Applications
  • Developing Jakarta Enterprise Beans Applications
  • Developing Hibernate Applications
  • Managing Transactions in JBoss EAP
• Configuration and Maintenance
  • Configuration Guide
  • Configuring Messaging
• Security
  • Security Architecture
  • How to Configure Server Security
  • How to Configure Identity management
  • How to set up SSO with SAML v2
  • How to set up SSO with Kerberos
• Cloud
  • JBoss EAP Management Model
  • Using JBoss EAP in Microsoft Azure
  • Deploying JBoss EAP on AWS
• Reference
  • Management CLI Guide
  • Login Module Reference
  • Performance Tuning Guide
  • API Javadocs

This issue involves using the EJB client to access EJB deployments, specifically using the EJB client's EJB/HTTP protocol (which requires support from Undertow), in a context in which the EJBs are deployed on a cluster of JBoss EAP servers and accessed via a load balancer.

So, the documents potentially relevant to this issue are Development Guide (mentions configuring EJB client), Developing Jakarta Enterprise Beans Applications (describes EJB/HTTP) and Configuration Guide (describes configuring high-availability as well as configuring JBoss EAP as a front-end load balancer).

In looking for sections of the documentation related to the homogenous cluster requirement of EJB/HTTP, I think the only suitable place to comment is here:

In Chapter 5 of Deploying Jakarta EJB Applications, "Invoking Session Beans", Section 5.7 "EJB invocation over HTTP" describes how to set up the client and the server to make use of the EJB client protocol EJB/HTTP.

It would be appropriate to add a section 5.7.1 "Using EJB/HTTP with a load balancer" to clarify that when using EJB/HTTP with a load balancer, the backend servers should be clustered and the deployments within that cluster need to be homogenous (the same deployments on every node in the cluster). Saying something about what to expect whien this does not hold (i.e. HTTP 404 repsonses) would also be appropriate.