[Moto X4 Questions & Answers] KrisM22:
newbie warning: don't re-lock bootloader, and beware flashing any custom ROM. &OTA...

only modify a phone you are willing to throw away.......

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pre-note: TWRP 3.3.1-0 -> fastboot boot twrp.img (this is temporary)

before doing anything, backup some little partitions

: EFS, fsg, Vendor. Maybe others. You will need these to get back to a working stock.

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DO AT YOUR OWN RISK - I TAKE NO RESPONSIBILITY.

note added 2-27-2020: it may be that some problems with returning to stock are due to not (in TWRP) advanced wiping data, system, dalvik ART cache before flashing. You can do temp "fastboot boot twrp-3.3.1-0-payton.img" w/o quotes, and do it there. -changed/edited. don't use TWRP to flash a stock zip!

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NO FIX IS KNOWN FOR ANY OF THESE PROBLEMS. PHONE IS DESTROYED.

newbie warning: don't re-lock bootloader, and beware flashing ANY custom ROM.

On the X4, the bootloader changes drastically between 8 and 9 as it introduces a dual file system which is used by OTA updates to alternate the live system, and as a backup if failure. It is not a true Treble system, only partial. You must not depend on being able to flash back and forth between O and P. If you update to P, stay there. I expect this to be exacerbated by those phones which update to 10, if that in fact happens(probably One/fi only). There is also much confusion as to which file system/setup any custom ROM uses, and thus, how you would get back to stock, if that is even possible. Be very careful and assure yourself that you are fully willing to lose permanently your new phone before you do anything. Please read posts in these forums.

I've seen many posts of folks, mostly noobs, who have flashed ANY custom ROM Lineage and are unable to get back to a working stock. Sounds super simple but apparently it's not. Best to assume that if you try things, especially Lineage, that you will never be able to get back to a working stock. Read a bunch of posts here and you will realize that.

I've also seen a bunch of folks on this phone, and other phones who have run a bat file to flash their phone which contains the line

"fastboot oem lock" or similar.

Don't do it!!! - This will lock your phone and you will never be able to do anything with it again. It is totally unnecessary to lock your phone. Folks who should know better are leaving bat files lying around with this command. If you use one of those bat files to flash your phone, just check and remove that command line. Else you will have destroyed your phone. That's one of those things that "sounds good" until you do it.

EDIT: You can run stock on a bootloader unlocked phone - I do it all the time - plays PoGo just fine. I don't know about banking apps - I don't use them as I assume any 10-year-old can and will hack my phone.

EDIT: 6Feb2020: folks are reporting taking a security OTA onto a modified phone and rendering their phone(s) unusable. Only take OTA to a pure unmodified (no Majisk ever on it)(etc)(no mods ever on it)(stock recovery)(etc) stock ROM. Heed this warning. All of these "temporary" mods leave traces that screw up the update process.

EDIT: this was successfully fixed. see: https://xdaforums.com/moto-x4/help/ota-update-endless-fail-loop-ppws29-69-t4045771 my guess is only works if you haven't changed bootloader or file system - NO custom ROM.

NO FIX IS KNOWN FOR ANY OF THESE PROBLEMS. PHONE IS DESTROYED.

Please do a lot of reading here before you try to modify your phone, unless you are totally willing to render it useless. A word to the wise.