Joining game #126264361 on frankfurt.
While Possessing my opponent, I played a Spell Scroll to gain a Cursed "Swap" action card. After gaining the card, the curse, and the loot, the game stuck saying it was "waiting for Yardbird" (me) even though I was in the middle of playing my opponent's turn. I assume it was trying to ask me to play the Swap that I just gained from Spell Scroll, but there was no dialog or option for me to play it. I tried switching to my perspective by clicking my name, but it still said "Waiting for Yardbird".
Yes, if anything prevents a card to be gained by the Spell Scroll player, that will confuse the game and result in the scenario you described :(
It can happen if a card is gained, but by another player (in your case, due to Possession) or if no card is cheaper (with extreme cost reductuion).