It may happen that your simulation, live trading, or anything else you may be doing is not working as expected. The first thing to do in such a case is to turn on the Formulas & Conditions layer of the corresponding session and look around within your workspace. Errors are signaled with a red circle surrounding the relevant node of the workspace. Hover the mouse pointer over the node and you should get a description of what is that is causing the unexpected behavior.
Bear in mind that when the slider is fully closed, errors will no longer show up in the design space, as shown in the below video: