BME 680 and BME 280 Not Reading Constant Humidity

I am using the BME 680 and the BME 280 in a sealed glass jar. I know the absolute humidity in the jar is constant because it is sealed.

However, when I get my data from the sensors and calculate the absolute humidty, I am not getting a contant absolute humdity. I have been getting data from the jar being indoors at room temperature and at atmospheric pressure.

Is this because of how the sensors work? Are they not made for monitoring a small, enclosed space? If it is because of how the sensors work, I need to know why this is happening so I can account for it in my calculations.

Thank you for your help!

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