I use normal humidity of 55-60% so that may not have been your 1st problem. I use 65-70% humidity the last 3 days of lock down.
Do you have at least 2 temp/humidity readings in your bator? I have 2 - 3 with my hatches. I have had the opposite problem this year, having a hard time keeping the humidity up to 50% and I am in southern Texas where it is HUMID.
I really think it has more to do with keeping the temps and humidity levels stable throughout the waiting period, until its time for lockdown, and get your dates right on that. Every year is a different scenario, because it depends on the weather, where you hatch, your bator, etc.
Bator hatching is a gamble, we are trying to emulate a broody hen and sometimes we don't do so well. Actually, we just don't do as well as they do. They were born to it.