When my character is jumping and falls on the moving platform with a box collider the character seems to fall through the ground. I can see the character under the platform for maybe 1 frame and then it´s above again.
Have this problem already half a year but have no clue what the reason could be
Because you’re using ‘Discrete’ collision detection which is fast but moves bodies according to their velocity then, if they are overlapped, it solves them. Therefore, whilst this is fast, it allows overlaps or, if the body is moving quick enough, for it to pass completely through.
You can use ‘Continuous’ which sweeps the body/colliders through space detecting the exact collision point. Whilst this stops overlaps or it passing colliders completely, it’s more expensive to calculate therefore it should be used sparingly when it matters.
http://docs.unity3d.com/ScriptReference/Rigidbody-collisionDetectionMode.html
Are you using Rigidbodies?
This problem is sometimes caused when you use a Rigidbody but try to also try to manipulate the transform values of the object directly.