Whilst going through Antorus on my main yesterday I get a LUA error from the Kill Feed quite a few times. This seemed to occur when a player in the raid was killed by an NPC but I don't have more specifics than that. Interestingly enough, did some testing on a healer alt in LFR and intentionally let people die but couldn't recreate it at that point.

Error comes from here specifically.

However, despite pointing at that line my gut feeling is that this may be caused by taint elsewhere.

did some testing on a healer alt in LFR and intentionally let people die

All for the greater cause!

Will try and see if I can replicate this myself also.

Definitely an issue in raids when people died. But it's damned hard to work out the root cause. Not sure specifically why that function is failing.