I've had the same problem you had when I first got this game. Usually the slider thinks you are currently tapping/sliding on it, if its dirty or has something on it, like food crumbs or something. So what I would suggest is to clean your slider right when you start having that problem with the missing note sounds to prevent failing the song. And if that's not the problem, make sure to check on your batteries to see if its used up or need to recharge it if you have the Charging Station.
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numark idj2 reviewProject Management Blog
