Player movement problem

Hi everybody, I've got a strange problem with the movement of my player: I create a simple movement logic in the update function of my player script that checks the position of the player to increase his velocity after a specified position and manage player's jump. When the speed increase or the player jumps the player stops his run (when the player jumps it complete the jump animation and then stops). If I remove this logic (increase speed and jump) and I leave the code that set the speed of the player's rigidbody using a simple myRigidBody.velocity = new Vector2(moveSpeed, myRigidBody.velocity.y); it works without any problem. Do you know where is the problem? Thanks in advance