I bought a month ago the Artillery Genius. Everything was pretty good until today, I was printing a test cube and it stopped pulling out filament, when I looked the temperature it was -15 °C, a few seconds after the thermistor sensor broke and got stuck on the extruder creating a little bit of smoke. I had bought a thermistor sensor and a heater cartridge original replacement. I changed both and turn the printer back on. As soon I turn it on the extruder start to increase the temperature, almost 300 °C and then change to -15 °C. I checked the connections multiple times, I even change the sensor with another one, but nothing works. I checked the boards, cables but everything looks great. Don't know what else can be. I already contacted customer support but just want to look for another opinion while waiting for there answer.
Your printer does seem to have a firmware problem and lack important safety features - it should have stopped the moment it went 300°C measurement, beeped like hell, and shut down with an error message about Thermal Runaway Protection. Immediately stop using the printer!
Before you try to print again, you need to make a proper firmware for your printer, one that has both Mintemp, Maxtemp as well as Thermal Runaway Protection actiive and flash that. While setting up your firmware, make sure you use the right temperature table for your thermosensor. How to do that is detailed here.