Welcome to the thread! Everyone who is hatching is welcome.
Do you have calibrated thermometers inside the incubator? One of the first lessons to learn is to never trust the readings on your incubator.
Grandma got her job because she's my oldest hen, and one day after rain, she got a huge glob of mud stuck to her toes. I brought her inside and got the glob off, and was thinking about retiring her to freezer camp because she really wasn't laying much anymore. Then the power went out. I had 4 day old chicks in the brooder. On a whim, I put her in and watched her closely to see how she'd react. She was a good grandma, so now her retirement is to live with chicks indoors for the rest of her life.