So likely warm enough for Seramas. Special housing concerns shouldn't be an issue. You may want to stay away from RIRs. They tend to be the bullies of a mixed flock.
I don't think they'll be able to pass it.
I've butchered several chickens with a piece of glass or nail imbedded in their gizzard. The contracting gizzard just buried it into the meat and was destined to stay forever, till death do they part.
How old are your Cayugas?
My only concern is that young ducks need 2 to 3 times the niacin as chickens need. It says a waterfowl and chicken food but doesn't really declare the amount of niacin. I would probably ask the manufacturer how much is in it. 18% protein is probably sufficient.
Not putting water in till the end means just prior to pipping.
Who told you not to put water in and what has the humidity been all this time?
You want to add water during incubation to maintain the proper weight loss throughout.
What species are you hatching (ducks, geese, emu) and what has the weight loss been up to this time. Have you candled or weighed?
Those variables need to be known for a correct answer.
If chicken, hatching is overdue. In general if hatching is imminent, I'd say to go ahead and up the humidity...
IMHO, failure to thrive can become a thing in any species. My first guesses would be genetics, nutrition and disease. Among other lesser common causes can be incubation errors and age of breeders.
I assume the parents are your birds?
Talk about their age, nutrition of parents, especially egg...
I wouldn't use the potting soil nor the DE. Problems with both.
The DE is composed of minute crystals that can lodge in the respiratory system. The potting soil will take too long to break down into appropriate dust size particles (read that as a couple years).
I mixed sand with regular garden...
So I'm gathering that eggs from the same source hatch under a broody but not in an incubator?
If that is it in a nutshell and you are sure of your thermometers, it could be frequency of turning. Frequent turning the first 2 weeks is critical. Does your Govee have the means to download the...
Could be dozens of things. I've had sudden death on occasion. While there are a number of things that can cause it, all mine have been from heart attacks as determined by necropsy at the veterinary college.
As for your incubator being trash, it could just be faulty readings. Unless you are using a calibrated thermometer, you can't trust what the incubator says. Same for a hygrometer but not as critical as temperature.
Also, cheaper incubators with low wattage heat elements (40 watt) and fickle...
The first 2 weeks of incubation is the most critical for turning. Do so as frequently each day as possible. A minimum of twice per day but 10 or more is better.
I know this is water under the bridge at this point but in the future, I recommend sealing cracks with liquid skin bandage. I've used bees wax and nail polish - both without any success but most I've repaired with liquid skin hatched. One even fell and had cracks over 60% of the shell at about 2...