Well, Bruce, I am not an expert but I think you should edit the properties of the resource (I cannot be very accurate in the terms I use because my menus are in a different language, sorry...), and watch the dates of start and end of rhe quiz.
Several times I forgot to set a date for closing the quiz, so it gets the same dates for start and end - usually the time and date of the creation of the new resource. I think you must activate the editing mode, and then click the little hand icon in front of the quiz you need to edit; that will take you to a window where you can change the start and end dates.