Triangulating in my model app was my first fix to this problem. However, in order to save on the geometry in the modelling app I did rather locate the problem areas and rebuild them manually. So, now I know that the problem is created by polygons with 5 or more vertices, something that can create problems for some applications. But, as import worked in Vue4Pro I do expect that it's supposed to work in Vue5 as well so I will report the problem.