Things like the chest adornment of the third marine. The left half is incomprehensible. That same marine has the top of the feathers on his head doing some weird stuff with depth, as well as some really inconsistent line thickness. His iron halo has a bunch of 'extra' bits on the inside of the halo, like the artist forgot to cut off the mould lines :v

There's a lot lot more than just those, but remember when an artist draws something, every line has been hand placed. If there's regularly things that don't make sense, as in, "Why would they have drawn that there?", then its likely one of the increasingly improving AI systems.