Apparently, every now and then the factory procedure for calibration fails. Some sanity checking would be advised.
You already mentioned a possible solution for your case. You see that the values are bad because the 85C are lower than the 30C readings. You can check whether there is a sufficient difference (based on experience) on the 1.5V values, and if not, try 2.0V reference. Or 2.5V reference. Of course only if your application won’t suffer on a higher reference and your supply voltage is high enough.
Alternatively, you can calibrate the sensor on your own and store the values in info memory. But I doubt this is convenient J
