When Pepper Flash is installed and Plugins are enabled via

webEngineView->settings()->setAttribute(QWebEngineSettings::PluginsEnabled, true);

Right-Clicking into any Flash content (for example http://flash-movies.funmunch.com/movie-4.html ) causes the QWebEngineProcess to ASSERT.

The problem occurs in 3rdparty/chromium/ppapi/host/ppapi_host.cc, inside PpapiHost::OnHostMsgResourceCreated at

  // Run through all filters until one grabs this message.
  std::unique_ptr<ResourceHost> resource_host =
      CreateResourceHost(params.pp_resource(), instance, nested_msg);

  if (!resource_host.get()) {
    NOTREACHED(); //  <----------- HERE
    return;
  }

In release mode and also when you continue execution in debug mode, the WebEngineView becomes dysfunctional - you cannot navigate anymore. It still reacts to some things though - the css resizing of the links on the left is still done.