Bricking in the Locked-Bootloader Era: An Empirical Study of Modern Android Custom ROM Failures

The Android custom ROM ecosystem remains largely guided by anecdotal experience rather than empirically validated failure models. This six-year longitudinal study investigates system failure and bricking mechanisms during AOSP-based custom ROM installations across represen- tative mid-range Android devices: the Xiaomi Redmi Note 7 (Qualcomm Snapdragon 660) and Xiaomi Redmi 9 (MediaTek Helio G80). Covering Android versions 10 through 15, over fifty con- trolled failure induction trials were conducted per condition to characterize soft bricks, near-hard bricks, and hard bricks requiring chipset-specific recovery tools such as Qualcomm Emergency Download (EDL) mode and MediaTek SP Flash Tool. A critical finding demonstrates that performing a factory reset from Android OS without an installed custom recovery can result in a complete hard brick. Additional failure modes include recovery corruption–induced boot- loops with automatic stock recovery reinstatement, recovery state persistence behavior, and post-recovery network authentication failures linked to IMEI data persistence. Results indicate that flashing via custom recovery is significantly safer than fastboot-based flashing, and that kernel-level rooting frameworks (KernelSU) provide superior stability and security compared to boot image patching approaches such as Magisk. This work formalizes community knowledge into experimentally validated principles for safer Android device modification.