IAQ status is good, but the behaviour is still the same - worse air quality after venting, eCO2 is far away from real CO2. What does that mean? The sensor doesn't work properly?
eCO2 output from BSEC library is derived from IAQ output value. So they are related. If the air from venting contains some other VOCs caused by paint, motor oil, etc., then IAQ will become worse after venting which will cause eCO2 to get worse.
If possible, please provide the data log from your tests.