Collision polygons and origin image points are very important in Platform behavior. Your enemy sprite has different collision polygons in different frames. So when animation is playing or when the sprite is mirrored, it may suddenly overlap solid objects, which can cause different problems.
Make sure collision polygons are symmetrical and origin point is in the middle of the sprite (horizontally). Another very common solution is to use a separate invisible rectangular sprite with Platform behavior, and pin your character sprite to it.