2 cubes bounce off terrain, third cube passed through it, all have same x and z, just differing y values. Is this a problem with a setting?
all of the cubes hit the same spot on the terrain
I think you will need to upload a simple example.
I would guess that that your third cube has the greatest y value and your problem is either your cube dimensions/and or mass is too large; you are not keeping a reference to the 3rd cube shape or it is a timing issue.
Swapping cube2 and cube3 y values should be a start to assist in debugging.
So, the objects all have the same mass and fall at the same speed. Some bounce off the terrain others fall through it. The debug drawer indicates that the terrain is solid, and is in fact just a large cube with 0 mass. I've attached the code. The cubes that are falling are a mesh made in blender - is it possible that the problem is with this mesh? Though I just exported the default cube, so I don't see how that could be it.