Unfortunately I have been down this path for years and years. Baking the sensor in accordance with the manufacturer’s recommendation will bring the sensor back into calibration temporarily, but if you live in a high humidity environment, these Sensirion sensors simply have a wet dewpoint/humidity bias that I suppose is just a limitation of the technology. They will struggle to reach 100% at saturation and will read 5-7% high in humidity and 3-5°F high in dewpoint in the mid to low range. If you calibrate with software slope and offset as best you can, when the humidity dries out for an extended period, the high bias is reduced and your corrections will be artificially low. I’ve searched in vain for a better solution, but it appears one does not exist at the moment. I still have two analog Davis sensors that performed much better, but sadly I can’t find a 2 pin thin film capacitance humidity element that will work on such low power. The original elements are pretty tired. I might just have to move to the desert …