Using JBoss EAP 7.2.3.GA (embedding Undertow 2.0.15) to render a JSP-based application, we are getting the following exception:

Caused by: java.lang.IllegalStateException: UT000139: Exchange already complete
at io.undertow.server.HttpServerExchange.addExchangeCompleteListener(HttpServerExchange.java:941)
at io.undertow.server.handlers.MetricsHandler.handleRequest(MetricsHandler.java:55)
at io.undertow.servlet.core.MetricsChainHandler.handleRequest(MetricsChainHandler.java:59)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:274)
at io.undertow.servlet.handlers.ServletInitialHandler.dispatchToServlet(ServletInitialHandler.java:219)
at io.undertow.servlet.spec.RequestDispatcherImpl.includeImpl(RequestDispatcherImpl.java:391)
... 270 more

This error message was already addressed in https://issues.redhat.com/browse/UNDERTOW-1078 and is also referenced in the following https://access.redhat.com/solutions/4207321

Disabling the statistics as suggested doesn't help.