Geckolady
I'm not one to hatch eggs, but do have some knowledge about instruments and how they work.
Your eggs did not make it this time around, but there may be multiple reasons.

A very viable possibility, is your
temperatures displayed on your incubator were somewhat off. That means that even though they showed 99°F , the actual temperature could have been
higher or
lower. The way to treat this problem, is to do a test run and determine the actual real temperature at the setting you have.
Example1; you have it set at
99° and the actual temp inside is
95°. You would them proceed to add
4° to your setting, and see what the actual temp results. You would end up with a reading of
103° but your actual temp would be
99°.
Example2; set at
99° but actual temp is
103°. You would lower your setting to
95° and see what actual temp you end up with.
I am just using the
4 degree difference value as
just an example. Your test may have different results.
Remember that the thermometers used in these incubators are mass produced, and are
not LABORATORY ACCURACY.
I feel that people grade thermometers are much more accurate, and are in the correct range as well.
This is the type I would recommend, and my reasons.
View attachment 2361982
The whole thermometer can be inside incubator.
The other types of thermometer,(digital electronic) are accurate also, but I don't know if the electronic portion being inside incubator would be good.
View attachment 2361986
I also think.. that button needs to be pushed to show display reading.
Best way to conduct your test is using 6 eggs from grocery store. They wont hatch of course, but will operate incubator under real conditions. Testing with no eggs may throw off real actual operation simulation.