When reading the CGNS file, an incorrect topology result was obtained, but there was no problem using Paraview to read it. What could be the reason for this?

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I use the following code to read CGNS files：

    vtkNew<vtkCGNSReader> reader;
    reader->SetFileName(toUTF8(filename).c_str());
    reader->UpdateInformation();
    reader->EnableAllBases();
    reader->EnableAllFamilies();
    reader->EnableAllCellArrays();
    reader->EnableAllPointArrays();
    reader->EnableAllFaceArrays();
    reader->Update();

    vtkDataObject* obj = vtkMultiBlockDataSet::SafeDownCast(reader->GetOutput()->GetBlock(0))->GetBlock(0);
    vtkUnstructuredGrid* grid = vtkUnstructuredGrid::New();
    grid->DeepCopy(obj);

Then use vtkDataSetMapper to render the vtkUnstructuredGrid object.
I got the following result：

vtk_result
vtk_result939×607 189 KB

As shown in the figure below, it is clear that the result obtained in ParaView is the correct one.

pv_result
pv_result1759×1075 176 KB

I want to know what causes this discrepancy? How can I fix this error?