While trying to view the Lightstone of a Nightmare and the Lightstone of a Pale Figure in the House of Knowledge light chamber, the placeables would display the usual messages, but no illusion or recording would play.
Not sure whether the issue is related to the lightstones themselves, the lightstone chamber, or the character placing them (Ainsley Dyn, Rogue, acct Certified Retrievals @ 7PM today, module version 1910).. Maybe something else? who knows!