If the player's camera looks ~45 degrees up, then when throwing a grenade, the sound of hitting the surface will immediately be played
Watch the video: https://youtu.be/WIjMPQb0bmQ
yellow spheres show the main values of the angle of elevation to get this bug
If you throw several grenades at an angle of 45 degrees the sound of the impact when thrown has gone
As soon as we turn away and aim at this sphere again the on throw impacts will appear again