Maybe it's the lineup. You can grab the nade more easily if you stop crouching once you're clipped in the floor, so release the CTRL key and throw the nade while aiming at the white texture on the wall (a little bit to the right of your lineup in the video). Then press the +use key to release the grenade, and once it has exploded, you can shoot the smgnade at that black spot on the floor (or maybe at the upper black spot) and crouch again before saveloading. ALSO, I think you have to lower your FPS to 30 (bind y "reload; fps_max 30") after saveloading the second time.