Same here, It happen to me twice.
The first time I just used Ifont to change system font, reboot to system, then hang on 1+ logo, go to twrp, delete xpoded-modulelist.txt..... Still bootloop, hang on 1+ logo.
And I can't boot into TWRP (3.0.2.1) after that , try many times, sometimes it's luck to enter TWRP, but I can't mount system/date, can't advance wipe cache/dalvic/system/data, can't dirty flash rom.
Then I fastboot flash TWRP, may be boot into twrp sometimes , but still can't mount every partition in internal storage.
Finally fastboot flash stock recovery, wipe with stock recovery, try to adb sideload ota.zip with stock recovery, I have try both stock OOS and H2Os, both stuck at 47%, I almost give up. And think about return phone to China.
I give it a chance:crying: :crying:, fastboot flash TWRP (3.0.2.0 official), and it work , I dirty freedom OS and it can mount the system, after system reboot, no data lost, just like run a normal aroma dirty flash.
It's very strange.
The second time, I just flash TBO black theme on some system app, It happen again!!
Reflash TWRP both version serval times still cant boot into TWRP or mount data/system, almost give up again. But after a stock recovery wipe, it auto boot into system sucessfully ! All my data is the same and google hangout black flashed, but root access lost, and I am with stock recovery.
I don't know 1) it's relate to not Wipe cache/Dalvik Cache after system/data changed
or 2) exf4/FAT problem format like this
https://www.youtube.com/watch?v=VJRKuQf0puE
Now i just went to get back my root access and won't flash anything till it clear.
(at least need to fastboot flash TWRP then flash superSU.zip with TWRP)