Helllo. I'm having this exact problem with BME688 & BSEC2.0 .
Migrated my code from BSEC 1.4 to BSEC 2.0 (ESP32 board) and now IAQ Accuracy is always 0.
I'm using "BSEC_SAMPLE_RATE_HIGH_PERFORMANCE".
And in "setConfig" I'm using BSEC provided configuration file "bsec_serialized_configurations_iaq.h"
I was wondering... In BSEC 1.4 I used a configurating file (generic_33v_3s_4d) which configured, among other things (I guess), the sample rate (lp), the sensor voltage (3.3v) and sensor history (4days). Those configurations are not needed in BSEC 2.0 or it's supposed they're included in bsec_serialized_configurations.h?
I'm also having problems when try to use BSEC 2.0 in any other mode than HIGH_PERFORMANCE. For example, if I change the sample rate to BSEC_SAMPLE_RATE_LP as I was using with BSEC 1.4, I got the following error: BSEC error code : -12. Which according to bsec_datatypes.h means:
"The sample_rate of the requested output (virtual) sensor passed to bsec_update_subscription() does not match with the sampling rate allowed for that sensor"