In my opinion a MKT order that doesn't get filled when it should have been means that the platform doesn't work. Is not an API issue, because even if I place the trade from TWS GUI is the same, even 20, 30 minutes to fill a MKT order.
I don't rely in paper trading to test the strategy, I did backtesting, and used it on other platform, but I have to test the integration of the strategy into the platform, , connection, data, orders and others.
