the mesh is in blender, it's correctly named in the slots and the flexbodies, and the slot is selected in game, but there's no error message and it doesn't appear:
it might be to do with the fact that the flexbody was on the group "GT_2400_chassis" and not "GT_2400_body"
Certainly, but if you have chassis nodes present it should appear, just to be binded to chassis nodes, I think. Haven't tested so much about changing groups though, not certain if slots and node group can have such dissappearing effect. However if you don't have group of nodes that is group flexbody is bind to, then it will not appear and if there is too few nodes it complains about VY node or XY node not found.
