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Tried with downgrading TWRP + twrpsarer : I was able to dirty flash 17/08 build, but Google services kept crashing at first boot, after reboot I went into bootloop and TWRP...
Then I had the SAR mount error and couldn't flash back to the 16/08 build...
Flashing TWRP 3.4 ended in no recovery at all (maybe my falt but I don't know how).
All in all I had to flash TWRP via fastboot, and reinstall everything I did yesterday...
And I had to double reboot after formating partitions, in order to flash with TWRP 3.4.
But I am running 17/08 build now...
There is something wrong with your TWRP and builds nonetheless guys