I keep my humidity at 30 - 40% till lock down, then bump up to 65%. If you have condensation on walls/windows, the humidity is too high. But, what you are doing has worked, so... who am I to argue. But, if you find chicks making it to lock down, then dying before they hatch, I would suspect...
You could buy 10 different hygrometers and thermometers. You could buy the cheapest or the most expensive ones. It would not matter what brand, what price. If you do not personally calibrate them, you can't trust them. Most of all, you can't trust the meters that come with your bator...
What did you run humidity at until lock down? Any condensation noted on walls or window? Do your air cells match the chart based on their age? If you have not done the salt test with your hygrometer, and if you have not calibrated your thermometer against a known to be accurate medical...