Herald plays Necromancer plays Zombie Spy with an empty deck. Game freezes and says "Play from trash" with nothing clickable.
Originally discovered in #30253798. Reproduced in #30254218.
Thanks for the report!
Interestingly, the problem doesn't happen when you play the Zombie Spy directly or just via Necromancer on an empty deck.
I guess it has to do with the Herold playing the card from the top of the deck, and some bookkeeping going wrong.