Does every frame in every animation have the same colissionpolygon?
It's already visible from the one you posted that it only has one collision point at the bottom, which in my opinion could cause issues.
Also the collision-lines on your backgroundfloor aren't straight (is that intentional?)
I would recommend using a square sprite for the platform behaviour and pinning the animations on top of it, but if you want to do it this way, just make sure all colissionpolygons are the same through the entire animation, at least where they touch the floor and I would make the floor collision straight, just to be sure..