Not so succesfull clutch

Hi community,
I'm looking for the reason behind a not-so-successful clutch. I incubated 6 eggs at a temperature of 31.9°C. The first two pythons started pipping on day 65, and on that same day I cut the remaining eggs.
The problem was that almost all the hatchlings, except one, had poorly absorbed yolk sacs. The remaining yolk was really large.
I'm trying to figure out where the mistake might have happened. I'm 100% sure about the temperature, as I had both a thermostat probe and an independent thermometer directly in the egg box.
I incubated the eggs in vermiculite with a 50/50 water ratio.

I'd appreciate any ideas or suggestions.

31.9*C is about 89.5*F so your temp would have been fine. Did the neonates come out on their own quickly, or did they stay in the eggs while they absorbed their yolk sacks? Did you find any twisted umbilical cords that would have prevented them from absorbing yolks?

Thank you, bcr229, for your response. The hatchlings stayed in the eggs for another 3–4 days. There was no tangled umbilical cord. Two of the hatchlings were already dead when the eggs were cut open — as if they were too weak and couldn't manage to cut through. The inside of the egg was scratched, but there wasn't a single clean cut. Two of them, despite having unabsorbed yolk sacs, have rather large bellies — it doesn’t look like hard belly for now — and two are quite skinny. I'm still trying to figure out where something might have gone wrong.

It sucks to have a problem clutch because you only get one chance/year/female.

What were you using for a heating element and thermostat? How were you diffusing the heat evenly in the incubator? Where was the probe in the egg bin?

If I was to guess on the issue based on your original description alone: I would suspect that the heat distribution was uneven and you have different eggs at different stages of development. Since 31.9C is on the top temperature for egg tolerance...an on/off thermostat would be bad...with a proportional thermostat relying on perfect thermal distribution. In the event of a poor heat distribution: Some eggs would die from overheating (development interrupted), and some would be underdeveloped at the same point in time where others are hatching.

+Fun fact: Ball pythons have a short umbilical stalk (not a cord). This is a sturdy anchored structure. Upon necropsy: I have yet to observe a single case where I thought a compressed umbilical stalk was the cause of hatchling death. I suppose anything is possible though...

Lord Sorril, thank you for your response. I’m using a DIY incubator made from a wine fridge, with a heating foil and a Danitech thermostat – which I dare say is the most reliable thermostat in our region (Central Europe). Heat is distributed throughout the incubator using a fan. The probe inside was in direct contact with one of the eggs. Unfortunately, I don’t remember whether the hatchling from that specific egg turned out fine or not. I didn’t notice any issues with the previous 4 clutches. However, I’ll definitely focus on checking heat distribution and verify it through measurements – it does make sense.