@tech-support Thank you!
There is no longer a bad CRC error when extracting super.img 
However, it seems the preloader_k6835v1_64.bin preloader in the new spflash build is still with sha256sum 20304da386e66379eab9805b81372319bd5127c6493294d5b2fe21369002fdfc, which means it is not compatible with BraX3 phones of the new batch. It bricked mine. I was (hopefully) able to repair it with the new preloader shared by @daniel here, also available here, sha256: d9ec305e5cf8b786ba5f39cd1715f49e9e7eee903cc54ed490c581604a414661