I’m pretty sure this issue comes from a corrupted/misinterpreted data from the live weather data feed. And not really from MSFS Live weather engine itself. If it’s getting the wrong data to read, then the temperature would be simulated wrongly too.
Perhaps the Live Weather engine needs some form of safety margin. Like there’s a minimum and maximum range of temperature that it could simulate. If the live weather engine is getting faulty data that made the temperature fall out of those range, then it should just set to the minimum/maximum limit temperature set in those margin whichever is closest, which should avoid issues like this until they fixed the data source issue.