Check that the collision polygon and Origin image point are exactly the same in all frames and in all animations. If you have many animations, it's better to use a separate rectangular sprite with 8-direction, and pin your player to it.
If this doesn't fix the issue, please post your project file.
EDIT: Sorry, just noticed that you've already checked the polygons and image points. To be completely sure, try disabling the walking animation.
Do you have any other behaviors on the player, or are you changing any of its properties like angle/position with events?