it seems there is a mismatch between the datasheet and the driver source code. gas_meas_index_0 in the datasheet is positioned in the status register eas_status_0 at address 0x1d. Address 0x1e is not used obviously. In the source code (function read_field_data) meas_index is read from buff, which should be BME6080_FIELD0_ADDR+1, i.e. 0x1e.