Yes! It's something quite hidden though that depends on luck to appear. I could spoil it, but that would ruin the fun.
Hint: it's something to do with treasure chests.
I am going to figure this out, it is not the case of failure = mob because one of the versions I failed with broken chest result, and no mob spawned. Now my lock pick is 47, and I open chests with a roll of 2, I hope this is not the case. I was thinking "putting a little light" on the subject was the answer but I have been killing all morning with all that equipment on.