In which case sorry no idea what the issue might be.
The only other thing I might suggest is tapping into the SPI interface on the unit and using the Blueflash tool that you can download from the CSR support page (https://www.csrsupport.com/), note you will also need to use a CSR USB/SPI interface board as the SPI is CSR proprietary (https://www.digikey.com/products/en/development-boards-kits-programmers/programmers-emulators-and-debuggers/799?k=qualcomm%20SPI).
Regards
Matt