What causes this?

[Jota180]

Oi, Fudcom. Why has this bug popped back into my game (the holes in the chest armour)? It used to happen regularly a couple of years back and now it's started happening again and it only happens to this toon. If I switch out that piece the replacement item doesn't have this bug. If I restart the game a few times it eventually works properly.

http://imgur.com/a/VeM6P

[Odonoptera]

These weird squares can usually be fixed by switching your client's DirectX settings around.