there is no way out of this without s-off, I don't even understand why you are putting efforts on installing ota/guru reset/nandroid backup at this point.
you are on hboot 1.56 means you should try to s-off using firewater.
then you'll be able to remove the tampered flag and set the bootload back to "LOCKED" (not RE-LOCKED)
follow guide linked in my signature for going back to stock
try to s-off using firewater + arhd 31.6 rom
At the moment I only need to know if it's safe to update to the new 18.104.22.168 update while it's unlocked... I got TWRP installed but I know I have to flash the stock recovery in order to make the update work. But I'm afraid I'm going to brick it again if I lock it again, as I don't know if it's needed to let the update complete without any errors.