Chicks can't break through the egg shell!!!

[ChickenCanoe]

I see a few issues. First is nutrition. Too many extras will upset the nutritional balance, leaving the yolks of the eggs void of key nutrients needed for healthy development. Stop giving the cracked corn and scratch completely. Those should be used sparingly, as a treat or cold weather calorie boost. Layer feed is for actively laying birds only, and is a bit low in nutrients for a breeding flock. Switch to an all flock or flock raiser feed, with a calcium supplement offered separately.
The next issue is temperature. A forced air incubator should be kept at around 99.5. Even half a degree lower can cause delayed hatching.
Thirdly, your incubating humidity may be too high for your specific conditions. Start with a lower humidity level and adjust from there. Monitor the air cell development and adjust your humidity, higher or lower, based on the growth.
Last of all is your collection and setting method. If you are continually adding eggs to the incubator, you will have a harder time getting anything to hatch. Hatching humidity will kill eggs that still have weeks left to develop. Collect your eggs daily, but wait till you have enough to fill your incubator. Then set the eggs all at the same time.

What she said. I couldn't have said it better and from the information you've given, those are all your likely issues.
The nutrition jumped out at me too. As was said, a 100% layer feed diet is adequate to produce table eggs but perhaps a little light on nutrients for super vigorous embryos.
Insert an appreciable amount of corn and scratch and now you're almost deficient for producing table eggs. Screw around with optimal nutrition provided by a complete chicken feed (containing the correct balance of all the vitamins, minerals, fats, energy and amino acids chickens are known to need) and you're asking for trouble.
For all the corn and scratch you add, you're lowering the lysine, tryptophan, niacin, vitamin D3, zinc. All these things will retard growth of embryos and chicks.
If you want good hatchability, lose all the supplements except perhaps meat and fish scraps. Then perhaps add a poultry appropriate vitamin/mineral supplement to the water a couple times a week. Do these things 2 weeks before beginning and while collecting eggs for incubation and I bet your hatchability increases dramatically.
Another problem with feeding layer feed to a breeding flock is that excess calcium can negatively affect sperm motility of roosters.

I have a question for you. I have started weighing my eggs in grams. For the last two incubation cycles, humidity 30-40% temp. 99.5 forced air, I noticed that by day 18 my eggs had lost between 17-20% of their weight. I know the 'ideal' is 14-15%. Air cells are generally where they need to be, except in the case of saddles. My hatches have been reasonable, not great, 70%, (shipped eggs being a factor). Have you noticed a greater drop in weight with lower humidity and do you think it matters?

Humidity and weight loss are one in the same. So yes, lower humidity will cause more weight loss. Weight loss is more accurate than humidity since not all eggs porosity is the same and not all ambient humidity is the same.

 

[aart]

Weight loss is more accurate than humidity since not all eggs porosity is the same and not all ambient humidity is the same.

But what do you do about humidity level to accommodate the varying porosity/evaporation/air cell size within a batch of eggs?

Hey, @ChickenCanoe, did you ever read my article?

 

[ChickenCanoe]

Whether you use weight or humidity, the variability of porosity may be problematic in either case. If your eggs are of different breeds or from different sources, some eggs will lose more, some less. In that case you'll have to go for an average.
Ideally, it is always best to incubate all eggs in a setting to be of the same species, breed, line and even size. But we know that most people don't do that.
Even doing so, I've had outliers. You can't risk an entire setting for one or two that aren't losing enough or losing too much. So in the end it is what it is.

I did go through most of it and will finish it this morning between butchering roosters.

 

[Mraya]

Don't blame calcium. A vigorous chick should have no trouble breaking through an egg shell. There may be other contributing factors but it's 99.9% chance your temperatures are low regardless of what you have it set at and what your thermometers say.
If eggs are fresh, stored at the proper temperature, turned during storage, adequate frequency of turning during incubation, breeder nutrition is high, breeders are in their prime, then you can virtually calibrate a thermometer by how many days it takes a chick to hatch. Chickens hatch in 21 days, period. Earlier and temps are likely high. Later, temps are likely low.

In addition to @casportpony 's questions.
How long were the eggs stored? For every day of storage, hatching is delayed approximately one hour.
Do you turn during storage? At what temperature and humidity are they stored?
Do you have a turner or turn by hand? How frequently?
What kind of diet do your breeders have? How old are the hens/roosters?

Chickens hatch in 21 days, period.

I have a question do they pip at 21 days or hatch fully at 21 days?

 

[ChickenCanoe]

All variables being correct, they should fully hatch at 21 days. Meaning, set at noon on a Sunday, they should hatch at noon on a Sunday.
Variables include:
temperature
humidity
turning
ventilation
egg storage time, temperature, humidity, turning
age of breeders - not too young or too old (causing males with abnormal sperm or females with abnormal germinal discs)
health of breeders - disease free
nutritional deficiencies or excesses in breeders - especially hens
use of drugs or presence of toxins
parasites
day length

 

[Mraya]

All variables being correct, they should fully hatch at 21 days. Meaning, set at noon on a Sunday, they should hatch at noon on a Sunday.
Variables include:
temperature
humidity
turning
storage time, temperature, humidity, turning
age of breeders - not too young or too old (causing males with abnormal sperm or females with abnormal germinal discs)
health of breeders - disease free
nutritional deficiencies or excesses in breeders - especially hens
use of drugs or presence of toxins
parasites
day length

Thank You