We have found an unfortunate bug in the latest release; it's described in issue #531. It does not happen every time you run, but when it happens while you are watching the visualizer, you will see a broker's cash position go flat. The simulation continues to run, but the broker's bank account is no longer getting updated, and possibly other important things are not happening. It also dumps a ton of error messages into the log. We think we've tracked it down, and hope to get a fix out in a day or two.