If your WiNE or Playonlinux installation of Hearthstone or Blizzard's Battle.Net client has suddenly stopped working after an update, one thing to try is to check if a newer version of Wine is available and install that. This usually gets me out of trouble with my Playonlinux installation.
So, Blizzard is offering a gift to players for some reason (possibly for a bug, I forget). But on my Linux install (via Playonlinux), clicking the Gifts button at the top just brings up a blank screen. You are supposedly also able to claim the gift by logging onto battle.net in a browser. But where does one go from there? There's a "Gift history" option in your account settings section, but that does not list anything that is claimable.