Thank you for the detailed reply (patrioti

). I am not getting the exact same error with yours.
I am getting this: Secure Booting Error! Cause: boot certification verify
Actually I had this error the first time after I flashed the recovery.img with Flashify. After that if I try the above combos, my tablet just displays the LG logo and then turns off.
I am not sure if I am doing anything wrong, but this case is very possible

. Did you try the 3rd method by yourself and worked?
I guess I will have to deal with the adb method soon
Edit:
I tried the adb method too. Unfortunately, I got the same error ! Also I got this loki error:
http://prntscr.com/2gip3b
Is that normal?
It seems that the .img is being flashed properly but for some reason it won't let it boot into the recovery mode.
I will now check the dev options maybe there is one that blocks it or something..
Edit2:
I just installed TWRP for now. Looks good, so I have a recovery mode