BME690 sensor gas resistance issue

Hi, I am working with multiple BME690 sensors and am monitoring gas resistance values, I have observed a strange pattern in multiple sensors - initially the gas resistance value is settling around 700k - 800k in my setup environment (range and sensitivity is good) but suddenly the sensor has started giving value around 30k - 50k for same environment (gas resistance is never going more than 100k ). This has happened with multiple sensors, does this mean - the sensor has gone bad? cause the temp, pres and humidity values seem to be accurate.

Thanks