2d rigidbody stops on collision if velocity smaller than 1

I have a 2D ball moving towards a wall, at perpendicular velocity 1. when it hits the wall, instead of bouncing back, it stops moving, with its velocity reduced to 0. If the velocity is greater than 1, like 1.001, the bug does not occur, and the ball bounces back from the wall w/o losing kinetic energy (velocity is reversed). picture 1 is the ball starting to move towards the wall. picture 2 is the ball after it has hit the wall. see the velocity is 0.