[LeEco Le Pro3 Guides, News, & Discussion] fatguy1121:
I flashed the latest 20s Chinese ROM to unlock my bootloader and had trouble getting back to LEX727 19s ROM with a working SIM card, this what I did to fix it.

Goal: Get LEX727 back to 727 ROM from any Chineese Variant (LEX720) with a working sim card.

Logic: We need to get the phone back to as stock as possible so that we can flash dr4stic's ROM That will update from CN5.8.018s to US5.8.019s. First we need to install CN5.8.018s, but we need to do it from stock recovery, to get stock recovery back we use a TWRP backup made by suhridkhan, then copy the CN5.8.018s zip, rename it to update.zip and allow the phone to do it's thing It will take quite awhile to flash the stock CN5.8.018s ROM, but when its done we can then install dr4stic's ROM, but first we need custom recovery again, since we flashed stock recovery when we used the TWRP backup. So we reflash custom recovery (I recommend GrossoShop's TWRP as that is what worked for me, however others may work). Reboot into fastboot, fastboot flash recovery the GrossoShop TWRP, then we go back to recovery. Now we can install the upgrade ROM. Once the upgrade ROM is installed, we can reboot and we'll have a completely stock version of the LEX727 ROM with Stock Recovery. (oobe state)

STEP 1 INSTALL WORKING ROM

1. You will need a working ROM to copy the TWRP unzipped files to the phone (figure this out on your own, but you should already have something that works)

STEP 2 STOCK RECOVERY

1. Restore this TWRP backup

1. Send the unzipped files to your phone in TWRP/BACKUP/<Device_ID>/TWRP. (You need a working ROM to do this with USB, you can try adb pushing the .zip and adb shell unzipping but I had permisison errors. and found it easier to just move the files unzipped)

2. Reboot into recovery, Advanced Wipe everything except Internal Storage (where your backup is)

3. Restore from the TWRP backup, before restarting, do a factory reset wipe and dalivik.

4. Reboot, and you SHOULD be in the LEX727 Rom, however your sim card will not be recognized depending on the modem firmware you came from.

STEP 3 GETTING DOWN TO CN5.8.018s

1. Since we have stock recovery, we can now use it to flash down to the right Chineese ROM version for dr4astic's ROM update to work.

2. Setup the phone, and copy LE_ZL1_LEX720_CN_5.8.018S.zip, then rename it to update.zip

3. Install the update through the phone settings or browser. (It will take quite a while 15ish minutes)

4. The phone may reboot into an endless boot loop where it just keeps redoing the same startup flash, To get past this reboot into recovery and perform a "Clear data" wipe.

5. You should now be in the stock version of LEX 720 5.8.018s

STEP 4 USING THE UPDATE ROM

1. We need to flash a custom recovery again (I recommend GrossoShop's as that is what worked for me, however others may work)

2. Reboot into fastboot and flash your recovery software

3. Wipe everything, data included and reboot back into recovery.

4. adb push the update ROM and install it, wipe dalvik and do a factory reset wipe before restarting.

5. When you tap restart system from TWRP the phone will vibrate for about 7ish seconds, dont do anything, just let it do its thing. It will reboot and go to a black screen, then finish rebooting.

(this is perhaps the most risky step as we are returning to a stock ROM with stock recovery and might loose our unlocked bootloader)

6. You should get everything back to stock ROM with working SIM card and an unlocked bootloader.

note: I will be saving local copies of all the files required indefinitely, so if any of the above links break, I will re-upload.