Mi4C currently running 7.2.9 weekly. I'm trying to unlock the bootloader after upgrading to Android 7.0 from 5.1. But all attempts at flashing a downgraded version (libra_images_6.1.7_20151221.0000.11_5.1_cn and 7.5.3.0.LXKCNDE, which are both recommended by wolkenjaeger's guide) fails after 14...