Exactly, opening the incubator on any day does no harm in itself, same with candling and even handling or turning the egg...
The so called 'lock down' enigma has grown to a black and white set of rules well beyond it's purpose...
Lock down servers two purposes...
One it's a mental minder to remove or turn off any automatic egg turners that could injure or harm a newly hatched chick...
Two it's a mental minder to potentially increase the humidity for an easier hatch with less risk of shrink wrap...
Beyond that all the black and white don't do this or that during lock down is almost entirely hyperbole nonsense...
Fact is a bird sitting on the eggs can't count, she doesn't know day one from day 21 or day 28, her only real sense of time passing is when the first chick hatches... But, she does nothing different day 1 through the end, she does the same thing in the same way... Also birds can't really control humidity, in a real dry climate they have been seen drooling/spitting on eggs, but this is rare, they have no way to lower humidity... Thus if it's a 95° day and 100% humidity that is what it is that day, just like if it was a 95° day and 30% humidity it it what it is...
If you open your incubator during 'lock down' and are concerned the humidity won't go back up get yourself a cheap spray bottle and mist the walls of the incubator before closing it up or simply spray a few misting in the incubator, that will easily replace and lost humidity...
In short don't dread some long list of black and white lock down rules, most are nonsense...
To the OP, have you verified you temp with multiple thermometers in different locations inside the incubator? It's also best to simulate the internal egg temp vs air temp, there are multiple ways to do this, some buy 'fake eggs' with thermometers built in, others use those little dollar store water snake tube toys, I prefer using 2oz preemie baby bottles... With the thermometer in water it's a much more accurate representation of the internal egg temp...
This is a 4oz one that I have used for larger eggs like Peafowl, thermometer is just an example, I have a digital one with a probe in there when it's in the incubator...
Beyond that start a log of your incubations, if you hand turn log that, long them temp and humidity each day or multiple times each day... Note the source (local, mail order what hen/rooster combos, brand of feed the hen was given) and cleanliness of egg prior to incubation, were they washed or unwashed? How were they washed, log all that and more then try to see if there is pattern to your bad hatches... If you log all this you might start to see a pattern of what is working and what is not...
I've spent quite a few hours researching methods and techniques trying to get everything right, which is why it's so frustrating that I've failed to have a successful hatch. Honestly, I don't store my eggs. I use to store them indoors, have them in an egg carton, have one side of the carton higher than the other and rotate it twice a day, etc. I tried lots of tricks, except storing at a certain temperature since I don't have a fridge that I can use solely for egg storage. I found that my hatch rate with my broody hens using those methods was lower than if I simply left the eggs alone in the nest until they're needed, so I stopped doing all those special precautions. I do this and get almost a 100% hatch rate, every fertile egg under a hen hatches. Now, if the eggs are a week or older, I do store those, but I generally don't use those once they're that old anyways. I don't think I'll do hand turning though. I'm a full time college student, so really the only time I'm able to be home to turn the eggs three times a day is during the summer and winter break. I have a Forced Air Incubator Model 4200 
It's always nice to have other's that don't think lockdown is anything more than a time guidline.
