This bug is pretty bad, especially when entering deep bodies of water.

When you enter the ocean, or a deep body of water requiring you to swim, while holding a gun (like the M4 as shown) you get this bug where your character starts freaking out, jittery, glitchy, as well with your M4 flying and glitching around your body.

This can also result in game crash, so yeah, video evidence shown below.

(By the way, reproducibility is always, but game crash, and character being jittery, glitchy, is random, M4 flying around body however is always reproducible)