Leggendo il 3D di FLippy498 su XDA (sarai daccordo con me che trattasi di una MUST to HAVE per il nostro M9) si legge nella FAQ punto4:
Vuoi vedere che il bootloop sia partito dalla versione di SuperSU 2.82 # da quella consigliata 2.65 ??Q4: Which versions of TWRP and SuperSU are the recommended ones?
A: The answer depends on your current firmware version. If you're using firmware 4.x then you'll find your answer here in the FAQ of the TWRP thread. (Click here, if you can't find SuperSU 2.79 SR3.) For firmware 1.x and 2.x the recommended versions are Captain_Throwback's Beta 1 of TWRP 2.8.7.1 and SuperSU 2.49. For firmware 3.x the recommended versions are TWRP 3.1.1-0 (official) and SuperSU 2.65. Using different versions than the recommended ones will probably lead to a bootloop. The M9 isn't compatible with the ramdisk changes that get executed by many flashable system-less SuperSU versions. However, updating the SuperSU app and its binaries via the Play Store after flashing one of the older versions is safe.
Bah ... la prox volta per sicurezza metterò la 2.65