satellite23 If you have separate animations assigned for jump, fall, land, idle etc I would check that the frames for each animation are the same size, that the origin is in the same place on each and the collision boxes match. Otherwise what can happen is that on landing the animation changes, the new animation is overlapping the solid object and so has to pop itself out.
An alternative to having the platform behaviour assigned to the animated sprite is to assign the platform behaviour to an invisible sprite object that remains a constant size and then pin the animated sprite (without platform behaviour) to the invisible object. You do all the platform and collision checks on the invisible object.
If that isn't causing the issue then we have a mystery on our hands and it would be worth sharing the cp3 file