@veye_xumm
With your setup in mind it seems that the issue can be in my adapter, main board or 31 pin FFC cable connection. I will continue investigation of the issue possibly with another main board and adapter. Thank you for your advice so far.
Also, I've noticed that GX manuals for Firefly and Orange Pi mention FFC cables that connect camera to the board directly and GX-MIPI-IMX662 Data Sheet page tells the camera now accepts I2C 1.8V level. So I think I will try direct connection as well.
