You haven't looked at all the possible causes of failure.My incubator is a Amazon sold Life Basis, which appears to be just a Janoel 10 with an automatic turner.
My first hatch was ebay quail and I got a near 75% hatch of the fertile eggs. Not bad for my first ever incubation. I used the dry incubation method.
My next 3 attempts at chicken hatches have been disasters. In each group, only 1 chick hatched.
The chicken eggs come from my flock, a combination of OEGBs, domestic RJF, white leghorns, and Wyandottes. A large range of different hens and roosters so lots of varied genetics.
I used the dry incubation method on the first chicken attempt, then standard temperature and humidity parameters for the next two hatches. I have cleaned the incubator well between attempts with alcohol, soap, and diluted bleach water.
Each batch consisted of 10 eggs. On all of the clutches, all of the eggs were alive developing at the end of week one, half had died by the end of week two, and the rest die between weeks 2 and 3, always except 1 chick.
I have tested my thermometer/hydrometer and confirmed its accuracy. I don’t know what to suspect except a ventilation problem, a problem with how the eggs are turning, or perhaps contamination with a chemical. First time I cleaned the incubator I used some sort of wet wipe, not thinking about what chemicals might be in it.
There are only 3 small vent holes in the bottom, only about half a centimeter across. They are on a thin lip that is barely lifted up off the desktop the incubator sits on. The unit’s fan sits on the top of the unit in the center and pulls upward.
Do you think I’m on the right path suspecting a ventilation issue?
I wouldn't start modifying a new incubator without eliminating other causes.
After all, it hatched quail just fine, why wouldn't it hatch chickens without modifications?
A fan should circulate the air inside the incubator not pull air in or push it out. That would be excessive ventilation.
With what you describe, the first place I would look is at your breeder nutrition.
What do you feed your birds?