ARCA is killing me! I have been using it to trade SPY exclusively since ISLD shut down but many times my orders are not executed TWS returning an order invalid message. These orders can be market or limit. It often happens when I place a sweep order a dime or so outside NBBO. WTF IS THAT? SMART quotes are always crossed plus it's slower. I didn't get filled this am on SMART after PMI, the market just took off . IB has to fix this ASAP, but help is clueless says never heard of that problem !