First it seems to me the controller is working and that 25C or so away from 500C seems to me quite good after the initial period of heat up. Would you please leave for longer and find out how close the oven temperature settles to 500C?
Jogged by Westward10's post I am thinking about the error in measuring the oven temperature PV introduced by the connection of the thermocouple's red and green leads to the metal terminals on the back of the controller. These two connections are the other half of the thermocouple circuit. A thermoelectric circuit has a hot sensing end thermocouple and a cold reference end thermocouple. T
he combined circuit produces a voltage/current proportional to the difference between the temperatures of each end. See:
Thermocouple Cold (Reference) Junction Compensation - https://blog.beamex.com/thermocouple-cold-junction-compensation
The reference thermocouple made by the terminal connections will reduce the voltage produced by the hot end. Thus temperature measurements by the hot end thermocouple will be seen by the controller as lower than they actually are. The controller has a an SC value for correcting sensor measurement errors so I will come back to you later about entering a value other than 0.
The problem is that the reference temperature 'cold junction' is actually getting warmer and warmer as the oven does because the terminals are enclosed in a space near the oven and ssr.
How accurate does the temperature need to be for your purpose?