A sample project to find a bug/wrong configuration.
This builds a test.war for Liferay 7.4.3.81 with mvn -P cdi clean install
The test.war is based on
com.liferay.faces.archetype.parent 6.1.1
with Portlet 2.0 and JSF 2.2 and CDI Integation.
It still uses Primefaces 6.1.
This project has three portlets Test 1, Test 2 and Test 3
That are shown in the menu.
But if Test 2 is selected, Test 3 is displayed
Debugging shows an javax.servlet.http.HttpServlet.service call at line 623, but HttpServlet has neither in javax.servlet-api-3.0.1.jar nor in release.port.api-7.4.3.81-ga81.jar that line.
It looks like at least the wrong _title "Test 3" was set in the portletResponse during that call.