I tried the .cap and had a quick look at the events, I'm not sure what's causing it. The way to find out what causes a slowdown is to back up your .cap and delete things until the framerate jumps back up.
My best guess is you use hundreds of sprites instead of a tiled background for the floor. You really really really really should use the tiled background objects instead of tiling hundreds of instances of sprite! With hundreds of sprites, every tick anything requesting a collision check (like the platform movement, which requires several every tick) has to iterate collision tests over hundreds of objects. With a tiled background, it makes one collision check, and then it's done the whole tiled background area.
If it's not that, though, then you should try the removal approach.