The floors are grid-like and when the player goes from one Box Collider 2D to another he sometimes gets caught and stops. Additionally, sometimes the transition sees the player getting ungrounded, triggering the jump animation instead.
Try using Edge Collider 2D instead of Box Collider 2D. However, if you still want to use Box Colliders, you might try setting the Edge Radius value to something like 0.001.