Ambient temperature may be the issue. My house does not hold a steady temp. I moved it to a warmer area for the second batch. I keep a blanket or sweater wrapped around it but am careful not to cover the vents. I think I have the same thermometer you are using. I’ve ordered another thermometer...
Well I have had nothing but bad hatches with the Kebbonixs incubator. I am not sure why. This last time I went with my digital thermometer because I didn't trust the incubator, First hatch in the bator was 2 out of 12. This year using the digital instead I got 3 out of 10 eggs to hatch, better...