Do you have windows open with fluctuating air in the house? If so, that can be contributing to the issue. They operate best when the room retains the same temperature, when around 70 degrees. When adjusting the wafer for small changes, it's 1/4 turn or less, and you have to wait an hour before you can see if the adjustment was too much or too little. Basically baby sitting, one small turn up or down at a time until it holds steady. But it won't hold steady if the room temp changes dramatically through out the day, in the case of open windows.
It may not be an issue to the eggs, you should get some to hatch, as long as the temp never stayed too low for too long, or too hot. They may hatch early if it was consistently too high, or hatch late if the range was usually under 100. When you replace the wafer, lay several towels over the eggs to retain heat during the project. That will give you some more time to work, about an hour, maybe more.
The incubators are ventilated on the bottom, and subject to change when the air in the room changes. It might still be the wafer, if you have ruled out room air and how often you adjust it. Adjusting it too frequently, more than 1/4 turn, can become an endless hassle. I've had tiny 1/8th turns help stabilize them, a full 1/4 turn being too much.
Good luck!
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