[G4 General] sdembiske:
*See the Addendum at the bottom of this OP for The Solve*

This thread has arisen from a particular issue that was originally thought to have arisen* by flashing a pre-rooted system image that was prepared following the method outlined by Senior Member hackarchive in "Root ANY LG G4 Variant 100% Success Directives | Root Injection | Less Bricks" (https://xdaforums.com/g4/general/lg-g4-100-root-success-directives-root-t3180586).

*later proved by Senior Member steadfasterX to be an erroneous assumption.

The issue: The H812 LG G4 (that has an un-lockable bootloader) that came from the carrier (Canada's Roger's/Fido) with Marshmallow (H81220x) installed. It was rolled back to Lollipop H81210h originally with the pre-rooted H81210n system image flashed after - the reason: both the stock and pre-rooted 'h' versions did not have the last stagefright vulnerability patch whereas the 'n' version did, hence an added level of security. However, no one had a confirmed Roger's/Fido stock H81210n kdz (Rogers/Fido is the only carrier in Canada that has the VoLTE option included and operational for the LG G4) that anybody could find a link to and

when an exFAT formatted SD card was put in the pre-rooted 'n' version, it failed to recognize the format (no problem with FAT32)

whereas it was recognized in the rooted earlier released 'h' version

. The 4gb restriction size of FAT32 did not allow the backup of the system image with Senior Member steadfasterX's "TWRP-in-FiSH" (https://xdaforums.com/g4/development/locked-twrpinfish-locked-g4-devices-t3573048) to the external sd card given the FAT32 size restriction. The exFAT recognition issue originally appeared to have arisen with the pre-rooted 'n' version when the missing original stock kdz was installed through the refurbish method with LGUP-NEW without an SD card installed or when the original system image was extracted OR, as steadfasterX has suggested, it was originally for a phone with a different kernel.

At the suggestion of steadfasterX and thanks to his work on this issue, the effort to reverse-engineer and revert to stock from the root-injection method itself has been undertaken. The work is all his, the testing to date and soft-bricking getting to this point, are mine.

Make no mistake ... this is a work-in-progress and soft-bricks and other risks, always a possibility

What you have here is a link to steadfasterX's latest revision to help unravel this issue that should not change anything if the DEBUG setting is left as it is: DEBUG=1. Follow his instructions exactly. I have run this version with DEBUG=1 with absolutely no problems and no issues rebooting after - no actual changes were made to the phone when the DEBUG=1 mode was used.

Note

: Changing the 1 to a 0 will allow actual execution of the script and is not advised at this time*.

* Not advised at all as it will = Soft Brick.

Refer to the following link: https://xdaforums.com/showpost.php?p=72837723&postcount=343

but please, post to this thread only if you are interested in helping/testing/solving or have any questions etc.

Thanks.

S.

Addendum

: Credit for The Solve ...

Full credit for the solve goes to ReeS86- refer to his post @ReeS86

Special Thanks to all the work by steadfasterX he put into helping us get to this point.

For a quick and easy method to get an exFAT formatted SD card recognized in the pre-rooted Rogers/Fido H81210n system image: see the Addendum in my post @sdembiske