have no clue why they disappear, is the stick to thin? the disappearing one in the video has mass 0.02kg, principle moment of inertia/mass 7e-4, 7e-4 and 7e-6.
Or should i reduce the simulation timestep? now is 3ms under ode engine.
the scene file is here
Thanks for any suggestion
objects disappearing are usually the result of the physics engine writing/computing bad values for object positions/orientations. In your case the objects that have disappeared have an illegal position (e.g. NaN, not a number). You can also provoke this by writing Nan-type values to object positions, inside of a script.
Try to monitor specific values to see if you get something funny just before an objects disappears (the object will however still be visible in the scene hierarchy).