If I understand correctly, your platform is a KinematicBody and you you want it to stop when it collides with something? What can the platform bump into that would make it stop? Platforms may support only one-way collisions, so do you want the platform to stop when something lands on it, or is it a block that supports collisions in all directions (like bumping into a wall)?
First of all, if you are using Tweens to move a kinematicbody using their
position member, I think that is your issue as to why collisions aren't occurring.
move_and_collide are designed to move Kinematicbodies and have them stop when they bump into something.