How do I Stop my Platformer from getting stuck in the ground

I have made a few platforming games before and I have never has this problem, when my platformer is running, it gets stuck in the ground. It is not placed inside the box of the solid platform, and it only happens for a small amount of time. When the platformer stops getting stuck in the ground, then it dips up and down when running. There are no animation frames on the sprite yet.

Upon messing around with settings, when I turned on poly frame, I saw how skewed the collision frame was.

Have you an example for that? Capx or HTML.

Do you use an invisible rectangular object as player and pinned the animation sprite to it?

Sounds like an issue of the collision box.