I guess there is nothing wrong with your project; you just get a warning from the type that informs you that the flow in at least one time step through the pipe is greater than the volume of fluid it can hold. That's just information, an advice to remember you that you shouldn't model an hydraulic loop where the flowing fluid in one time step is greater than the volume it can hold. The fact that your controller is not stuck seems to indicate that you are not in this situation, maybe thanks to other components in the same loop. In your case I will not be worried, best regards
Angel