Undertow random freeze (java.nio.channels.ClosedChannelException) when calling remote EJB

In multiple environments we have a separate front-end(s) and a back-end server, all JBoss EAP-7.1.0. The front produces seemingly random freezes when calling servlets that make EJB calls. Then the front-end recovers after 5-10 minutes. This can happen with multiple front-end servers at the same time or individually.

We already fixed a catastrophic freeze by creating a new worker thread pool just for EJB: https://access.redhat.com/solutions/3138871
But the issue with temporary freeze remains.

At the end of the freeze, we get this exception in the server.log:
13:33:33,710 ERROR [io.undertow.request] (default task-12) UT005023: Exception handling request to /thc/policyenforcer/pages/loginB2C.jsf: javax.ejb.EJBException: java.nio.channels.ClosedChannelException
at org.jboss.ejb.protocol.remote.EJBClientChannel$MethodInvocation.handleClosed(EJBClientChannel.java:1163) [jboss-ejb-client-4.0.9.Final-redhat-1.jar:4.0.9.Final-redhat-1]
at org.jboss.remoting3.util.InvocationTracker.connectionClosed(InvocationTracker.java:222)
at org.jboss.remoting3.util.InvocationTracker.lambda$new$0(InvocationTracker.java:70)
at org.jboss.remoting3.util.InvocationTracker$$Lambda$818/1687208284.handleClose(Unknown Source)
at org.jboss.remoting3.spi.SpiUtils.safeHandleClose(SpiUtils.java:50)
at org.jboss.remoting3.spi.AbstractHandleableCloseable$CloseHandlerTask.run(AbstractHandleableCloseable.java:520)
at org.jboss.remoting3.spi.AbstractHandleableCloseable.runCloseTask(AbstractHandleableCloseable.java:425)
at org.jboss.remoting3.spi.AbstractHandleableCloseable.closeComplete(AbstractHandleableCloseable.java:286)
at org.jboss.remoting3.remote.RemoteConnectionChannel.closeAction(RemoteConnectionChannel.java:508)
at org.jboss.remoting3.spi.AbstractHandleableCloseable.closeAsync(AbstractHandleableCloseable.java:368)
at org.jboss.remoting3.remote.RemoteConnectionHandler.closeAllChannels(RemoteConnectionHandler.java:619)
at org.jboss.remoting3.remote.RemoteConnectionHandler.receiveCloseRequest(RemoteConnectionHandler.java:222)
at org.jboss.remoting3.remote.RemoteConnectionHandler.handleConnectionClose(RemoteConnectionHandler.java:119)
at org.jboss.remoting3.remote.RemoteReadListener.lambda$null$0(RemoteReadListener.java:55)
at org.jboss.remoting3.remote.RemoteReadListener$$Lambda$843/522103121.run(Unknown Source)
at org.jboss.remoting3.EndpointImpl$TrackingExecutor.lambda$execute$0(EndpointImpl.java:926)
at org.jboss.remoting3.EndpointImpl$TrackingExecutor$$Lambda$770/1542977483.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [rt.jar:1.8.0_45]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [rt.jar:1.8.0_45]
at java.lang.Thread.run(Thread.java:745) [rt.jar:1.8.0_45]
Caused by: java.nio.channels.ClosedChannelException
... 20 more

If you could provide any help, that yould be great.
Thanks a lot for your help.