I had a successful hatch just a few weeks ago. My only thought is that I am tilting it instead of opening and tilting the eggs, but that should not affect the thermostat itself.
I'm hoping the eggs are not so sensitive that an hour or so of fluctuating temps kill them off. After all, the hens don't all have the same body temp, just like humans don't.
Was it a still air or a forced air incubator? I would think the tilting the incubator wouldn't work with a still air, because of the air stratification. The only thing I can think of for forced air would be that maybe the thermostat mechanism doesn't adjust properly if it is tilted?