Anycubic i3 Mega incorrect Heated Bed temperature Reading
The first value, which is in your pictures 179 and 184&nbsp;°C, is the measured value. The 0&nbsp;°C value is the set value. It looks like the temperature reading from the hotbed is not working correctly. So there are two possible issues:


The cable on the backside leading to the hotplate might be damaged. This seems to be a common issue with this printer. You could check if the cables show any obvious damage.
The hotbed thermistor is broken. On the leads on the backside you can measure with a multimeter the resistance between the green an blue cables. Typical readings are in the range of 100&nbsp;k&ohm;. If you touch the thermistor, usually it is placed in the mid area of the heatbed, the resistance should change.