[solved] Temperature sensor way off?

What are you using to read? E.getTemperature or:

Bangle.getPressure().then(d=>{
  console.log(d);
  // {temperature, pressure, altitude}
});

The first uses the sensor in the Bangle's CPU, but the latter uses the altimeter chip which should be a lot more accurate.

... but even so the Bangle will take maybe an hour to cool down after you've worn it for a bit