Gain Bodeks got a few parts in it. He apparently ran quite a successful options mm operation but then it slowly stopped working. After months of reviewing their code it was all because of order types he wasn’t aware of. He also did a podcast with chat with traders but unfortunately they never discuss what these order types are. Just that they exist.
IEX is way better than nasdaq, they publish all the rules their matching engine uses, and peg orders are reinserted in the same order they were received, unlike nasdaq, where they just randomly throw cards in the air