Have you tried to use the quad and tris, on even just tries export option ?

Looks like Simlab or Sketchfab have trouble to redraw the super long ngones when using .obj format.
If you dont want triangulate model, you could try the 'divide larger than' option ... a value of 0.5 seems good here ... that will help to avoid very complex ngone.

.Obj is not very great for ngones export, probably the worse format in fact.
The model is rendered fine in Modo, using .lwo or .fbx format, with default export settings.