70% would definitely kill all eggs in my bator.
I have 100% hatch rates regularly but I mostly set my own bird's eggs which are fed well and have no disease.
I keep my humidity at 30-35% throughout and only raise it to 50ish when I see the first external pip.
One thing I notice is a lot of people spread the eggs out in the incubator.
I keep all of the eggs close together with thermometers and the humidity gauge as close to them as possible.
That way I can be sure the temp and humidity is the same (as close as possible) for all eggs.
I don't think...
I can't tell much about what causes an egg to quit but it does look like these made it far/almost to hatch day. I think humidity and ventilation are the only thing that is in your control that could cause them to quit late. The other things that cause them to quit this late would be parent...