Good news if you've already spent your 3 free Mirror Shards on the Arena last week! CD Projekt Red has refilled up to 3 free shards for everyone again because of the connection issues some players had experienced.
Quote from @PlayGwent
Due to connection issues in the Master Mirror’s realm, we tricked Gaunter O'Dimm into refilling up to three shards for everyone who participated in the promotion! They will be distributed within the next few hours. Have fun in Arena!
Also check out this week's episode of "This Week in Gwent" below: