Hello AnnaB,
BMP280 is used to measure barometer, the test results are approximately linear with the actual air pressure. But at the same air pressure point, it will be affected by temperature. The data sheet contains the description of compensation, and the sensor API contains the compensation code.
For your issue, if you confirm that your hardware complies with the HSMI specification, you need to keep the same software with the reference code software, and then look at the test results. https://www.bosch-sensortec.com/media/boschsensortec/downloads/handling_soldering_mounting_instructions/bst-bmp280-hs000.pdf
... View more