Section plane in exported animation

I’ve worked with sketchup pro to a lot of animations and I’m having troubles in the last one I’m working on.

Basically I’ve a section plane that shows a group of things from one scene to another in the middle of a longer animation.

With the preview inside SU everything works fine but atfer I’ve exported it seem like the material are turned to transparent or invisible and the only things I can see is the shadow they cast.

any hint?

All section planes are setted correctly and all the layer are switched on and off correctly.

Many thanks