A couple people (depending on settings) have had problems at Erlking's bookcase, not realizing they could scroll down to see/read the book he was thinking of.
Actually, a fair number of people have gotten stuck at about this point. More people have had trouble with the fight with Laiken, though, so (as you found) that would have shown up much more in your search, depending on which terms you used and over what time range.
After mindreading the mute goblin, reading his writings gives you a couple of stat points; that may have been the book that disappeared (IIRC it was on the end table closest to the door).
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