qt5+vtk9.0,vtkGenericOpenGLRenderWindow::render() seems to be working incorrectly

I copy an example from github,the name is " SideBySideRenderWindowsQt".But the graphs just flashed and disappeared.then if I call function qvtkwidegt->GetRenderWindow()->GetRenderers()->Render(),the graphs will appear again,but if I call function qvtkwidegt->GetRenderWindow()->Render(), the graphs will disappear. Is there some problems with vtkGenericOpenGLRenderWindow::render() or some else problem?

Where are you getting the example from?

This example SideBySideRenderWindowsQt should work for you. This works for Qt5.15.1 and VTK 9.0

FYI: This site has many examples and is maintained: vtk-examples, this section, in particular, may be useful to you: Qt

Here I get the example.
Now ,I change the emvironment,QT5+VTK8.2,then the problem solved(There are some other problems yet).