Hotend drops to 175 ºC once extrusion starts (MINTEMP error reported) Hotend drops from 205&nbsp;&deg;C to 175&nbsp;&deg;C, and then the printer errors MINTEMP. How can I fix this? Fan is not starting yet.

#define  DEFAULT_Kp 28.65
#define  DEFAULT_Ki 2.80
#define  DEFAULT_Kd 73.33

#define HEATER_0_MINTEMP 5


MINTEMP is 5&nbsp;&deg;C? It's impossible it's getting that cold.
Sudden drops in temperature curves like in your picture are usually missing readings on the thermosensor:

Disconnecting the sensor from the board registers as min-temp of the sensor while shorting out as max-temp, so it triggers the mintemp/maxtemp security protocol: shutdown.

One could disable mintemp/maxtemp protection, but that wouldn't solve the issue. The issue is usually the wiring of the sensor. To find the fault, put temperature on the sensor but keep the motors disabled. Watch the read temperature. Move the printhead manually and slowly. If it suddenly drops and throws the error, you might have a faulty lead close to the printhead. If not, you need to open the electronics box to check if the connection to the board is ok. In the worst case, you might need to exchange the whole temperature sensor.