In the post above, the sensors were contaminated during the assembly process. If your BME680 were assembled on custom boards, please confirm that no harmful processes may have damaged the sensors.
To root out configuration issues, please confirm that you have successfully implemented the sample code available in BSEC's package, and that both timings and communication on the bus is truly as expected in your code (e.g. with a logic analyzer). If your setup allows it, you could eventually try your current SW implementation, but while connected to BME680 shuttle board instead of the on-board sensor.
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