Is the incubator in a climate controlled area? That could affect your temps if it's not. There may be other factors. Call it beginners luck but I just hatched (Monday into Tuesday) 6 out of 7 eggs. This was my first attempt ever to incubate any type of eggs. Mixed breed chickens in a homemade Styrofoam cooler incubator with a dimmer and an incandescent bulb. I didn't turn them more than twice a day. Sometimes only once per day. Twice the light bulb burned out including Saturday morning, right before they hatched, when I found the incubator was at 70 degrees and the eggs felt like ice cubes. But they survived, thank God and an answer to prayer. My humidity was all over but basically low to 60% for first 18 days and 50 to 75% until they hatched after that. It was a sloppy job for sure, but it worked out fine, thank God.
The points are: temp variations could be external. Occasional wide temp variations didn't kill my hatch. Humidity wasn't as critical as I'd feared it would be.
Finally, I ordered last week a Hova-Bator 1583 (? It has the digital temp and humidity) and the egg turner 1611. I've been setting eggs in it while my homemade incubator was approaching hatch. The Hova-Bator is nice. No turning by hand, steady temp, no bulb to burn out, fan-circulated, humidity fairly easy to control. FYI. YMMV. But it cost about $190 delivered. My homemade incubator cost me about $30.
Best of luck and said a prayer.
--HC