[LG K10 Guides, News, & Discussion] Darkos333:
How to flash/reflash superSU (extended instruction):

So, I managed to successfully install superSU (and Xposed) on my LG K8 (K350n) with instructions supplied by gottlasz, but it worked only once.

After few weeks I failed badly while playing with some theme-editing apps (I tried to use Gravitybox and few other apps to modify softkeys - dont repeat my mistake guys, use G4 TweaksBox instead, works like a charm) and I ended up with unstable system. So, fresh system install was the only option for me (I had no full backup, now I know it was stupid move to not make it).

After reinstalling system with LG Bridge I could not root my device again - I did all the steps from original instruction correctly, but device just won't boot after this pesky "device corrupt" message that appears after unlocking bootloader. I spend dozens of hours playing with this problem on my own, and I finally managed to get things to work. So if you tried original instruction from gottlasz and it didnt work, perhaps my slightly different approach will help some of you. This is exaclty what I did:

1) Boot up your phone in download mode (connect via USB and press volume up key).

2) Use LG Bridge to reinstall your system (Software update -> Update error recovery). Be patient, this will take some time.

3) After your system has been successfully reinstalled, turn your device off and perform hard reset (press power + volume down, release power button after LG logo appears (dont release voulme down key) then quickly press power button again for ~1sec while still holding volume down). Do factory reset.

4) Wait for your device to boot up, do the first-time-setup as usual. Unlock developer options. Make sure OEM unlock is checked. Turn on USB debugging.

5) Boot to twrp just like gottlasz explained:

adb reboot bootloader

fastboot oem unlock (press volume up on device)

fastboot boot lgk8twrp.img

Do not skip bootloader unlocking, because reinstalling via LG Bridge re-locks your bootloader!

6) Now the tricky part. If you had installed superSU previously, or tried to install it before and somehow failed, there is a high chance that there will be unwanted supersu folder in your root directory. In TWRP go to advanced and run file manager. If there is supersu folder in your root directory - delete it. As usual, make sure you are only deleting supersu folder, otherwise you may brick your device, perhaps permanently, if you remove something else.

7) Also wipe your dalvik/cache. It may be unneccessary, but I did it anyway.

8) From this point perform gottlasz's boot recompressing procedure:

-mount sdcard, backup your boot image to it, unmount sdcard

-plug sdcard to your computer, repack boot image via karliv, upload gz-compressed image to sd card, also upload superSU (and Xposed if you want it) binaries, eject sdcard

-mount sdcard in your device, install gz-compressed boot image, install supersSU (and Xposed) binaries, backup your new boot image, unmount sdcard

-plug sdcard to your computer, repack new boot image via karliv, upload lz4-compressed image to sd card, eject sdcard

-mount sdcard in your device, install lz4-compressed boot image

9) Before rebooting to system, unplug usb cable from your device. Again, it may sound unrlelated, but thats how I did it, and frankly it never worked when I left my device plugged-in.

10) Reboot to system. My device boot-looped once, dont interrupt this process. After a while device should boot up normally with first-time-setup, with superSU (and Xposed) installed correctly.

Hope it helps, good luck ;)