Here some more information... we changed the loggin to debug on the cockpitengine, and this is the error extracted:
ERROR it.eng.knowage.engine.cockpit.api.export.CockpitExportResource.exportExcel:86 - Cannot export to Excel
org.apache.catalina.connector.ClientAbortException: java.io.IOException: Broken pipe
at org.apache.catalina.connector.OutputBuffer.realWriteBytes(OutputBuffer.java:353)
at org.apache.catalina.connector.OutputBuffer.appendByteArray(OutputBuffer.java:754)
at org.apache.catalina.connector.OutputBuffer.append(OutputBuffer.java:683)
at org.apache.catalina.connector.OutputBuffer.writeBytes(OutputBuffer.java:388)
at org.apache.catalina.connector.OutputBuffer.write(OutputBuffer.java:366)
at org.apache.catalina.connector.CoyoteOutputStream.write(CoyoteOutputStream.java:96)
at it.eng.knowage.engine.cockpit.api.export.CockpitExportResource.exportExcel(CockpitExportResource.java:81)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:139)
at org.jboss.resteasy.core.ResourceMethodInvoker.internalInvokeOnTarget(ResourceMethodInvoker.java:509)
at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTargetAfterFilter(ResourceMethodInvoker.java:399)
at org.jboss.resteasy.core.ResourceMethodInvoker.lambda$invokeOnTarget$0(ResourceMethodInvoker.java:363)
at org.jboss.resteasy.core.interception.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:355)
at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:365)
at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:337)
at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:310)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:439)
at org.jboss.resteasy.core.SynchronousDispatcher.lambda$invoke$4(SynchronousDispatcher.java:229)
at org.jboss.resteasy.core.SynchronousDispatcher.lambda$preprocess$0(SynchronousDispatcher.java:135)
at org.jboss.resteasy.core.interception.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:355)
at org.jboss.resteasy.core.SynchronousDispatcher.preprocess(SynchronousDispatcher.java:138)
at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:215)
at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:227)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56)
at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)
at sun.reflect.GeneratedMethodAccessor423.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.apache.catalina.security.SecurityUtil.lambda$execute$0(SecurityUtil.java:280)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAsPrivileged(Subject.java:549)
at org.apache.catalina.security.SecurityUtil.execute(SecurityUtil.java:311)
at org.apache.catalina.security.SecurityUtil.doAsPrivilege(SecurityUtil.java:170)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:221)
at org.apache.catalina.core.ApplicationFilterChain.lambda$doFilter$0(ApplicationFilterChain.java:145)
at java.security.AccessController.doPrivileged(Native Method)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:143)