Haven’t tested the fix yet, though, gotta look into it.
By the way:
https://hearthstone.wiki.gg/wiki/Legacy
Yesterday it looked like these bunglers forgot to add EXPERT1 to the list of eligible cards, ruining Day 1 of the mode (essentialy, only LEGACY cards were playable). The comment above regarding ‘Classic’ cards (indeed, cards from EXPERT1 are those that can be obtained from Classic packs) indirectly supports this theory.
PS Looks like they’ve fixed it indeed, but Naxx hasn’t been added yet, despite it being Day 2 on the EU server already. Are they compensating for the lost Day 1 or are they gonna add it later, I wonder?
PPS Naxx appeared after restarting the client.