I'd suspect a faulty sensor before anything else based on how quickly the temperature rose. Unless there's a heating element in your freezer, it shouldn't be possible for the entire space to warm that rapidly while closed.

I work in refrigeration. Your sensor is likely measuring air temperature. This is normal during a defrost cycle which will happen 1-4 times a day. Best recommendation, submerge the sensor probe in a bit of water. Not a huge amount, but enough to simulate "product" temperature and not air temperature.

Looks like what I might expect if someone added a warm item to the freezer right next to the thermometer.

Power prolly went our