Why is your temperature spiking? Whatever is causing that needs to be fixed.
Have you calibrated your thermometer? Are you absolutely sure it is reading correctly? Since your hatch was late, there is a really good chance your incubating temperature is too low.
Is that a still (or thermal) air incubator or a forced air (one with a fan)? If it is a forced air it shouldn’t matter where you take the temperature inside, but if it is a still air that is very important. Warm air rises. You can get a lot of temperature difference based on height in a still air.
A forced air can possibly have warm or cool spots, especially a homemade one.
Have you calibrated your thermometer? Are you absolutely sure it is reading correctly? Since your hatch was late, there is a really good chance your incubating temperature is too low.
Is that a still (or thermal) air incubator or a forced air (one with a fan)? If it is a forced air it shouldn’t matter where you take the temperature inside, but if it is a still air that is very important. Warm air rises. You can get a lot of temperature difference based on height in a still air.
A forced air can possibly have warm or cool spots, especially a homemade one.