I would have to look back as to why but I have heard that it's not a good idea to keep incubators on the floor.

For some reason I feel like it had something to do with air quality. Maybe someone else here knows.
That may or may not have anything to do with the quitters. Sometimes it just happens. For example, maybe some kind of stress on your flock. I have more quitters in the middle of summertime here. The eggs are all still treated exactly the same, aren't left out in the heat (usually), but it seems that different types of stress on the hens can also affect viability. I've been documenting it for a couple years and specific months of the year are the same with a higher number of early quitters and while I didn't document it as thoroughly I even noticed a difference from the same flocks when there was rain in the summer, it improved the viability, I'm assuming because of lower temps while it was raining putting less stress on the hens even though it was still mid summer.

Maybe I'll attempt a more thorough home experiment on this myself this year.
Anyway, I'm going down a rabbit hole, lol, my first step would be to elevate the incubator like you had it before.