I found a mutterlock chest, and based on the muttering voices, the solution would have been “vemp et maldus” but the chest vanished. “Vemp et maldus” was the only option on the list that had all three words so I’m sure its not that I got the order wrong.
I’ve seen some older threads complaining about the same bug, and it seems like it is still an issue. From what I’ve seen, these seem like a super rare event so I’m bummed to have missed out on it.