When loading bullets into a magazine on the current stress test version (version: 0.63.146661), the sound effect of a player punching the air is played instead of a bullet loading sound.
Also when unloading a magazine on the current stress test version, the sound effect of melee attacking with a sharp weapon is played instead of a bullet unloading sound.
I have tried this multiple times and it seems to happen every time.
(I only tested the Makarov and UMP45 magazines).