The reward is [Restoring Balm] and when I run my cursor over it in the quest log, I get this error in my chat window:

Error occured while running hooks for: GameTooltip.SetQuestLogItem 
Invalid quest item in SetQuestLogItem("type",index") 
Call Chain: 
 (tail call): ? 
[string "QuestLogItem1:OnEnter"]:4: in main chunk

I am using the latest -master release (I think) if that makes a difference.

I think it's not even an EQL3 problem, but rather that the quest has been patched on Nostalrius to have different rewards than it actually does in 1.12 - yet they didn't quite do it 100%, causing these issues.

Are you using EQL3?

I have Extended QuestLog 3.6.1 disabled and I am playing on Kronos. Are you implying EQL3 would fix the problem? Or were you trying to confirm it wasn't causing problems?

Also happens to me time to time, for various quest - rewards, not using EQL3 or any similar addon, playing on Kronos (no modified quests).

The thing that confuses me though is "Error occured while running hooks for: GameTooltip.SetQuestLogItem" isn't something that questie it's self could generate. it doesn't contain anything that would print "Error occured while running hooks for"

Gotta figure out what's causing it

Since I've seen that same message and I'm running Enchantrix and other tooltip addons - are you running some of these maybe?

Yes - EnhTooltip, Enchantrix, Informant

Maybe I can add something in !QuestieCompat to fix these issues, going to do some testing

There you have it.