The problem likely has to do with the meat thermometer. Check to see how accurate it is. if it says +\- 3degrees, the it can be off by a bunch. The other problem is the speed of detecting temp change.
It is better to get a thermometer that is made for incubation use.
The problem is with the 4200 w/autoturner.
They leave you no room to place thermometers without losing or jamming in the rack. The water wiggler with the meat probe therm ( that has an alarm set ) has helped me achieve very successful hatches.
I have no problems with them and they are closest to my calibrated therm which I believe over the built-ins any day!