Projectiles extremely inaccurate on our server

Aiming cross at the center of the wood block, bow fully drawn, never moving the cursor, distance: 16 blocks, this is the spread I achieve.

And this is my shooting from 32 blocks away, aiming at the upper edge of the wool target, horizontally center.

This abysmal accuracy doesn’t only apply to bows – all projectiles, including enderpearls, snowballs, eggs, fly with extreme amount of randomness, much worse than on any other regular server I played on. The difficulty is set to Hard. This happens regardless of TPS lag, network lag, or who’s doing the shooting. Achievements like "Sniper Duel" are a total pipe dream, at 50 blocks the arrows have several chunks of spread. Nobody, including the admin, has a clue why this happens, and how to fix it. Can anybody help?