50% humidity is the ideal humidity so like Food says that would not account for all the quitter which looked like they happened during week 2 of incubating.
Having an accurately calibrated thermometer is crucial - calibrating it with Ice is not a reliable method! so for the 100th time accuracy is vital for temperature - less so for humidity
this is how to know if your thermometer is accurate or not:
https://www.backyardchickens.com/ar...incubator-thermometers-and-hygrometers.73634/
To me the most important aspect is what was changed from the first incubation to the second incubation which did increase hatch rate slightly even if it was still only 30% that hatched.
Something improved! So you need to ask yourself what fraction of change happened to increase your success even if it was not the result you hoped for.
Did you have the incubator running for 24 hours before adding eggs. Did you bring the eggs up to the right temperature slowly over several hours before adding cold eggs to a warm incubator?
Did you leave the incubator open while candling eggs?
Is the temperature in your incubator the same all over the incubator - this is woth investigating by moving a thermometer around the incubator, let is settle for an hour then check. Some incubators need a certain ambient temperature so if the room temp is too low it can affect the temperatures, avoid fluctuating room temperatures or anywhere near a door or window.
To help you decide it would help to know when the 7 hatched- ie what day after setting the eggs. If they hatched early chances are the temps were too high, if they hatched late then temps might have been too low but fluctuating temps can cause this too
were you hand turning or using an automatic turner? Hand turning has always given me good results but you need to make sure you wash your hands every time you handle the eggs.