The error you saw is intialization error which caused on FW download error. either some bits are not correct or lost during communication.
The FW itself are well tested before release on BMI270 and we have example code in our COINES UI platform to show you how it works.
BMI270 can accept any length of burst write for the configure files but some MCU can only support some limited bytes for burst write. So you need to double check the read_write_len parameters when you use to initialize the sensor in device structure is matching to your MCU spec or not.
You can try to read out the configure string and compare to the one you written into then you will know if there is any communication error on the bus.