Lord Errant - Main Story Quest (Bugged for everyone)
Your companion's level does not scale, mobs in the quest have no enmity table (ie. attack your npc randomly one shot and kill them).
The quest has been broken since 1.19. It is virtually impossible without the help of a level 50 to oneshot all the mobs. I have had a 50 pugalist try to help me and we've still failed 19 times.
This has threads all over the forum about how it's still broken. This is a simple fix and I am surprised it wasn't fixed in the hot-fixes you recently applied