I've been having this problem ever since the Arena came out. I can build a deck just fine, play my matches fine, but when I stop playing for a few days, the Arena resets for me. I lose any money my deck has won, my deck is completely gone, and the simple tutorial arrows and text boxes pop up explaining how the Arena works. If I play it every single day, at least once, it never happens, only when I skip a few days of playing.
