Sphere collision "sticks" to Box collision

I have a sphere bouncing around in a frame defined by rectangular Box collisions. The walls and balls have a Physic material with zero friction and a Bounciness of 1, so it should technically bounce around forever. The ball gets no Y velocity, just X and Z. There is no gravity in the scene.

When the angle of reflection is extremely oblique, the sphere tends to "stick" to the wall, while continuing to move. For example, on a "vertical" wall (oriented screen up/down), its Z (up/down) velocity remains unchanged, but X (left/right) velocity will become zero. The ball can be "bounced out" with a third actor, but this is far from ideal.

According to scripts I have attached to the ball, no collision events are occurring. The ball is visibly intersecting the wall if the game is paused and examined.

Is this a problem others have encountered? Is there a workaround or solution?