Hi Pilou, did you have welding turned on when exported?

When welding is turned on, it should unify those points at the pole area so that those polygons there are all connected to a single 3d point.

If welding is turned off, then polygons in this type of situation can have their own individual points that are stacked up on the same location - this is usually the cause of the type of behavior that you show there.

Points must be shared between polygons for things like subdivision to cross over them.

But if you have welding turned off, I'm a bit surprised that the seam didn't also pull apart in a similar way.

- Michael