BrewPi (Arduino) Losing Control After Temp Ramp

Every time I ferment anything, the BrewPi always seems to lose control at the end of a temperature ramp. My setup is a chest freezer, with a small fan inside to move the air around. One Temp Probe is in a stainless thermowell, while the other is just hanging in “free-air” in the chest freezer. BrewPi Settings are set to the defaults.

Any ideas how I can fix this?

Have a look at this topic:

I explain why it happens there.

Also try searching the forum for Arduino + oscillation.