[Xiaomi Mi A2 Lite Guides, News, & Discussion] locovibe:
This guide was originally written by chief_os from 4PDA.ru on how to roll back to Oreo, but my network issues wasn't caused by downgrading and still this helped me out so big thanks to the guy from the beautiful Lviv.

I alter this guide a bit, according to what I've done to get my network to work.

Download all the given files:

Qualcomm Tool QPST_2.7.453.zip - unpack and install

QualcommIMEIRebuilder.zip (given in this thread)

daisyQCN.zip (given in this thread) - it contains the file daisy.QCN, which you will need to recover your IMEIs

Fastboot ROM image of your choice from here

TWRP Recovery twrp-3.2.3-0-daisy.img - move it to your ADB & Fastboot folder

Follow the steps:

Remove all your SIM cards from the tray followed by disabling PIN security

Make a screenshot of your IMEI numbers and store it outside the phone

Install QPST_2.7.453.0

Enable USB debugging

Unlock the bootloader with

fastboot oem unlock

and, if you don't want to lose your data, use the instructions with Vol- button given here.

Reboot with

fastboot reboot

Go to the dialer and open the diagnostic COM port by typing: * # * # 7 1 7 7 1 7 # * # *

If the code doesn't give you any feedback, type:

adb shell
su
setprop sys.usb.config rndis,diag,adb

Disconnect and connect the cable, then check the Device Manager for a device qualcomm hs-usb qdloader 9092 (COM[port number]). If the device is not there - reconnect again.

Open QFIL.exe and check what port is your phone on. If you can't see any, click on SelectPort and choose your [port number].

Choose Tools, then QCN Backup Restore

Check Enable Multi-SIM, click Backup QCN and wait for the completion of the current backup (if something goes wrong, you can roll back)

The backup file will be in the given folder

Run Qualcomm IMEI Rebuilder and select downloaded daisyQCN.qcn file

Replace IMEI numbers with

your IMEIs

and click Rebuild

Run QPST.exe. Choose Restore tab, select the rebuilded .qcn file and click Restore

At this point you might want to check if all is working as it should. If not, proceed:

Create a backup of the EFS partitions:

Reboot in Fastboot by:

adb reboot bootloader

Boot into TWRP by:

fastboot boot twrp-3.2.3-0-daisy.img

and after requesting the password, do not press anything on the phone

On the PC, type the commands in the given order:

adb shell
mkdir -p / sdcard / Backup
dd if = / dev / block / mmcblk0p39 of = / sdcard / Backup / fsg.bin
dd if = / dev / block / mmcblk0p40 of = / sdcard / Backup / modemst1.bin
dd if = / dev / block / mmcblk0p41 of = / sdcard / Backup / modemst2.bin
dd if = / dev / block / mmcblk0p42 of = / sdcard / Backup / bk5.bin
dd if = / dev / block / mmcblk0p49 of = / sdcard / Backup / persist.img
dd if = / dev / block / mmcblk0p50 ​​of = / sdcard / Backup / persistbak.img
exit
adb pull /sdcard/Backup/fsg.bin fsg.bin
adb pull /sdcard/Backup/modemst1.bin modemst1.bin
adb pull /sdcard/Backup/modemst2.bin modemst2.bin
adb pull /sdcard/Backup/bk5.bin bk5.bin
adb pull /sdcard/Backup/persist.img persist.img
adb pull /sdcard/Backup/persistbak.img persistbak.img

Click the recovery button when requesting a password, go to Reboot and select System

Check if your backup files are in the ADB & Fastboot folder

Reboot the phone in fastboot and type:

fastboot oem edl

Flash the ROM via the MiFlash utility or via command line flash_all.bat batch file (don't choose flash_all_and_lock!)

Reboot the phone, go through initial setup and check if your SIM cards are working. If not, repeat steps 7 - 12

Check Enable Multi-SIM, click Browse and select the rebuilded .qcn file. Press the Restore button

When done, reboot into fastboot by:

adb reboot bootloader

Repeat steps 18 - 19

Run the following commands in turn:

adb shell
dd if=/dev/zero of=/dev/block/mmcblk0p40
dd if=/dev/zero of=/dev/block/mmcblk0p41
exit

Repeat step 21 and boot the OS

Now everything should work just fine.

In case of anything goes wrong, you can restore your backup .qcn file via QFIL (12 - 13) and then reflash your backups

Load into TWRP and execute commands:

adb shell
dd if = / dev / zero of = / dev / block / mmcblk0p39
dd if = / dev / zero of = / dev / block / mmcblk0p40
dd if = / dev / zero of = / dev / block / mmcblk0p41
dd if = / dev / zero of = / dev / block / mmcblk0p42
dd if = / dev / zero of = / dev / block / mmcblk0p49
dd if = / dev / zero of = / dev / block / mmcblk0p50
exit
fastboot flash fsg fsg.bin
fastboot flash modemst1 modemst1.bin
fastboot flash modemst2 modemst2.bin
fastboot flash bk5 bk5.bin
fastboot flash persist.img
fastboot flash persistbak persistbak.img

Reboot.

In some rare cases you may still experiencing network problems. If so, check your EFS partition if it doesn't contain some weird looking folders. If yes - just delete them. [need to edit this part later].