I have noted that version 6.5.2 of OpenCascade has introduced some problems displaying the model taken from here . I cannot attach it here because its size (6.80 MB) is bigger than the maximum allowed size on this forum (2 MB); if you give me an email address that could accept its size I'll send you there.
In particular, if you see it using front view of Import/Export app and zooming it with the new version the surface doesn't appear right while with the 6.5.1 and with other CAD softwares it appears right.
I have the same problem with my app written with OpenCascade that uses another visualization library so probably the problem could be in the BRepMesh triangulator.
Thanks in advance and happy new year!