I've never actually had this come up, but I was thinking today about what would happen if you played a card that interacted with an encounter card that is immune to player card effects while the card is either in the encounter deck or in the encounter discard pile. Most of these immune cards are never actually in the encounter deck because they are put into play or kept out of play at the start of the quest, but there are a few locations that are in the encounter. For example with Out of the Wild; Could you remove the location from the game, or is it immune? Can you use Shadows of the Past to put the location back on the deck?

I'm guessing the answer is that you ignore the text on the card unless it is in play, but I'm not sure. I recall a similar ruling that said you can use Fortune or Fate to bring Beorn back into play. Has anyone resolved this before?

As you say, you can use Fortune or Fate or Landroval to interact with Beorn, so cards like Out of the Wild or Risk Some Light should be able to manipulate encounter deck cards just as well.

****... grand spleen is too fast.

Exact same thing

I agree with this interpretation, although to add up to the confusion, many player or encounter cards have effects that trigger even while "out of play".

They just need to have a text that explicitly specify from where (outside of in play) they happen... (with one or two exception...)