As Dreamora said don't use more than 4 weights. Tho from what I know I'd say don't use more than 2 whenever possible cause they will slow down the game a lot.
I'd also suggest to make sure to export the animation in a way that doesn't require to search for certain children to animate it. This will simplify loading of dynamic content.
To me it sounds like a bug in the exporter, as if it's adding a dummy top node. Animated meshes already have this dummy node, created by blitz when loading (note: EntityClass$ of the top parent is not "Mesh").
I'd also suggest to make sure to export the animation in a way that doesn't require to search for certain children to animate it. This will simplify loading of dynamic content.
To me it sounds like a bug in the exporter, as if it's adding a dummy top node. Animated meshes already have this dummy node, created by blitz when loading (note: EntityClass$ of the top parent is not "Mesh").