I have two versions of PCB that integrate BME280. I will name them as version A and version B. Version A is produced in July and Version B is produced in October.
I have two boards of version A and did a test in July on the readings of BME280 with comparison to other air sensors. The results were OK as the temperature, humidity and air pressure readings were close to the air sensors we were using originally. Both boards read ~29.5 degC and read 53~54% relative humidity while the reference board read ~31 degC and read 56~58% r.h. The reference board was at higher temperature because it had more other sensors and a cellular module.
In October, I used three boards of version B and did a test on the readings and found that their humidity readings were much lower than the reference boards at their own locations. At ~30 degC on both version B board and the reference board, the humidity reading was 15% lower. At ~44degC, the humidity reading was 22% lower than that on the reference board. At ~26 degC, the humidity reading was 12% lower.
Then I used boards of version A to conduct the test at 30 degC and 26 degC and got similar results. This contradicts with the result I got in July. These two boards were not used and stored at room temperature with >50% r.h. I am not sure if this is considered as the third method of reconditioning as stated in the datasheet.
What is the possible cause for having this problem?
As the boards are stored at room temperature with >50% r.h.You can follow the reconditioning procedure in the datasheet, and make sure that you have done the calibration:
Please provide the temperature and humidity log data you got in the test and the information about test environment and steps.