There’s a glitch right now in that when it’s the other player’s turn, and sometimes when it’s your own, you can click and hold the opponent’s card and it’ll let you see what they have even if you haven’t used a card to reveal their hand. This glitch works in both campaign and multiplayer at any time, including turn one, but it’s a double-edged sword as it will also cause the game to not allow you to take your turn after a short while. I was able to recreate it in arena against someone else (they were able to see my cards when they tried it) so it’s very easily doable, and hopefully easily fixable too.
Edit: It seems the game not allowing turns might be unrelated. It’d need more testing so I can’t be certain whether it is or isn’t as I just had a game do the same thing in the campaign even though I didn’t use the glitch.