[ZTE Axon 7 ROMs, Kernels, Recoveries, & Other Deve] Oki:
To avoid more device bricks I have created very detailed, easy to follow instructions on how to update with minimal risk. The Bootstack in the OP is fine, but it doesn't support Emergency Download

(EDL) mode. To avoid that I have gathered my custom B12 Bootstack, the TWRP Labs 1.3 and the Official LOS15.1 into an EDL package.

BACKUP:

if you want to keep your information, then you should do a backup of your data before continuing with this guide. You can use the file manager to move your Documents, Downloads, Music, Pictures, Videos, etc... from your internal storage to an external SD card. You can upload them to a cloud service such as Google Drive, One Drive, MEGA, DropBox, etc. Or use the USB connection to move your information to your PC.

DEVICE UNLOCK:

Unlocking your bootloader will trigger a factory reset, and will delete the internal storage along with all the information in your phone. If your Axon 7 bootloader is still locked, you have to follow this guide before proceeding to the rest of this guide. It works for Marshmallow and Nougat stock phones. Please use that thread to ask any question related to unlocking your device.

INSTALLATION INSTRUCTIONS:

WARNING, THIS GUIDE WILL WIPE ALL THE DATA IN YOUR DEVICE, INCLUDING THE INTERNAL STORAGE.

IT REQUIRES YOUR DEVICE TO BE UNLOCKED, OTHERWISE YOUR DEVICE COULD BE BRICKED.

!!! Whatever you do, it is at your own risk !!!
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In case you get stuck at any point in this guide, do not panic! There is a straightforward way to go back to stock. Just follow this Unbrick/Restore guide. I've tried to make things as easier as possible for everyone, specially newbies not used to deal with the Axon 7. So, I have created stable custom EDL packages. In order to reduce the risk and complexity, this one Stop ROM Shop performs all the following actions in a single flash:

- installs my customized B12 Bootstack with EDL support

- removes unlocked bootloader annoying warning message.

- creates vendor partition.

- installs TWRP Labs Mod 1.3 custom recovery

- installs Official LOS15.1 ROM.

- And the guide also helps you to format data and cache as f2fs in case you haven't done it already. It provides better battery, performance and extends the lifespan of the internal flash.

STEPS

Download and Unzip Axon7_LOS15.1_180925_B12Oki_TWRP_LABS1.3_FULL_EDL.zip to a folder in your computer, ensuring there are no errors. I have an A2017U, so the American modem is the package default. If you have an A2017 or A2017G just copy your modem firmware, from the corresponding provided modem subfolder, to the main folder. Just overwrite the default American modem file.

Install MiFlash in your PC. It includes the Qualcomm Snapdragon SoC drivers, nonetheless you can always install the latest Qualcomm drivers.

Enter EDL mode using one of the following options:

by pressing VolUp+VolDn+Power until the power led flashes briefly

Installing a terminal app and typing reboot edl at the app prompt.

connecting your phone to your PC and typing adb reboot edl at your computer's command prompt.

While your phone is completely off, press VolUp+VolDn while connecting your phone to your PC.

If you haven't done yet, it's time to connect your phone to your computer.

Open MiFlash in your computer.

Click Browse button and select the folder you created with the firmware files in step 1.

Click Refresh button and your device will appear listed as virtual COM port.

Click Flash button and wait for a few minutes until it finishes. Note the bottom options are not applicable.

Press VolUp+Power until the phone vibrates, then release both buttons and wait for TWRP to boot. Go to Reboot menu and keep pressed VolUp while tapping on DM-Verity ON until the phone vibrates. TWRP will restart.

Go to Reboot menu and keep pressed VolUp while tapping on eMMC Write until the phone vibrates. TWRP will restart.

Go to Advanced > Oki Labs menu and tap on Expand OS.

To ensure everything is clean you should format the DATA partition, including internal storage. Go to main menu > settings and ensure "Use rm -rf instead of formatting" option is not selected. Then go to Wipe > Advanced Wipe, select Data partition and tap on Repair_or_Change_File_System button and then on Change_File_System button. Select F2FS and confirm action. Do the same to apply F2FS to the Cache Partition.

NOTE: If you receive an error while formatting data, then go to Wipe > Advanced Wipe, select Data partition and tap on Repair_or_Change_File_System button and then on Change_File_System button. Format DATA as EXT4 first and, without leaving TWRP do it again as F2FS. That will fix the issue.

Go to main menu and reboot system.

Happy transition to Official LineageOS 15.1 Oreo. I have not included Google Apps and Magisk root since I just wanted to create a basic package with easy to follow instructions. If you are interested in expanding these instructions with GApps and Magisk just let me know.