Last night when I was checking the temperature using my medical thermometer and i tried placing at different locations in the incubator and each time the reading was different![]()
This article gives an interesting write-up on what is "normal" body temperature and how much normal body temperature can differ person to person and due to other factors. To convert 97 F = 36.1, 99 F =37.2, 98.2 F = 36.8 C, 98.6 F = 37 C. You might consider this when using body temperature to calibrate by.
https://www.webmd.com/first-aid/normal-body-temperature#1
A half a degree C high or low should not be fatal to all the eggs. It's not ideal but you should still get some decent hatches, they will just be early or late. The kind of temperature swings you are describing would be fatal. Does the temperature change that much if you measure the same spots at different times? Do you have something in the incubator that will block air flow?
If you had not seen that temperature difference I'd ask questions like are the eggs fertile, have you killed the embryo by how you handle or store them, or have you opened some unhatched eggs to see if or how much they developed before they died. I think you have identified the problem.
What is the make and model of that incubator? What you are describing makes no sense to me if the fan is working, but you are looking at it. My suggestion is to call the manufacturer or seller of that incubator and talk to them. I'm out of ideas.