No, the problem is it's a styrofoam box incubator and because the thermostat is not proportional the temp keeps raising a bit even after the heating is off (styrofoam keeps the temps very well), and then the thermostat turns on after the temp loweres, and it drops a bit below the set temp, before heating cable is back up to temp. So it's not the probe problem .
And I'm wondering if those small temp swings are harmfull for eggs?