What is wrong is enviromentally dependent. Your incubator - your fan or not, whether or not you DID calculate the differences in your thermometer and hygrometer so you actually KNOW real temps and real humidity. Ventilation at hatch is hugely important. Whether you had a water wiggler or fake egg temp to judge inner temp consistency.
Whether you drowned them because of too high a humidity and too low ventilation really is the most common killer and masses of unhatched chicks that are full term are a large indicator.
Low temps (throughout a hatch) because your thermometers were not accurate and not calibrated means many get to full term late and are too weak to hatch, foot deformities in survivors is a common clue there.
When you calibrate your measuring devices and you know your temps ran well and your humidity was on track for the method you are using and THEN you get a bad hatch, then you have the information you need to CHANGE things.
Your micro-climate in your house, yard, state are all different than everyone else's. The rules do not fit every house, just most.
If you hit on all the right criteria and STILL don't get good hatches - then start fiddling with what humidity you run at, and your ventilation.
Drop humidity first - try a dry hatch. If you've been dry hatching you can either try dryer or try for the higher humidity hatches.
If you have to "crack a lid" it might be better to just add more holes, two at a time is useful - opposite sides of the bator. Cracking a lid - having it not slide to far, or be too little cracked is inaccurate and inaccuracy is the death of hatches. Holes allow for consistent predictable levels of air flow.
Change ONE thing - air or humidity used each time. Changing two variables means you end up not know which helped or hindered a hatch.
If your thermometers or hygrometers were inaccurate and you've been using them and having bad hatches - find your accurate temps and humidity and do that first. If there is still failure - start with a humidity change, up or down in the next hatch.
While shipped sets of eggs often fail if they under went stresses or heat great enough to kill them. I've had zero, and one, and two survivors in shipped eggs. The more common averages are 60 or 70% and often higher in luckily well travelled eggs. I've had 100% hatches on shipped eggs.
Make sure of the accuracy of thermometers and hygrometers first. Use a water wiggler. Keep records. Change one thing at a time. For the duration of a hatch. You may need to do test hatches of unshipped eggs to refine things. I did. That way you're not playing with new things with really hugely valuable eggs.
Trying to fix things during hatches of hugely valuable and vastly more fragile shipped eggs makes for insanity.
If you can hatch one to two dozen at a time it helps to keep things stable and give you a better idea of %. When you hatch fewer you get less of an accurate assessment.
But repeatedly having mostly failed hatches means you shouldn't even be trying shipped eggs. It means you should be isolating your problems and solving them using cheap or free eggs.
Everybody loves free chicks - getting rid of test hatch chicks is pretty simple.
When you consistently hatch above 60% and hopefully into the 90's and a hundred, then you go back to trying bought eggs.
Running on in the low and no survivors is just repeating in errant hope.
You have to find what is wrong and what is right for YOUR set up. One careful step at a time.
Artificial incubation is an ART not a set of numbers someone calls rules. Keep at it but do so with an eye to changing what is not working.
An aside: to calibrate (check) your digital thermometer - if you use a contact thermometer (medical or instant read) they need to be IN CONTACT with a medium - inside a wiggler, in a fake egg made of silly putty, wrapped play dough (so it doesn't dehydrate) and have the medium in stable bator temperatures for at least 6 hrs before you check. Medical thermometers are contact based and more accurate than the digital ones. Once you know the difference in accuracy you can subtract or add to know the true temp the digital is showing you.
My digital with the probe in the fake egg - reads one degree higher than it actually is. If I didn't know that I'd be running the temps too low for the duration of a hatch. Since I know that I run it properly.
Small steps toward accuracy and then figure out the other problems.
