sigh... i keep discovering bugs in the worst way, the way that makes me lose rares.
so i was playing arena on my laptop and was mid string when i had to leave. so i just closed my laptop leaving the game open. when i came home, i forgot about this, and started playing on my dekstop, where i tried a new deck and grinded bronze for a bit, winning a pharoa (which i have been trying to get a set of for a long time) and a discord. i then closed it there and went back to my room, where i saw the game still on, so i finished it (lost) and when i went back to my deck screen, the pharoa and discord were gone.
i did a test to confirm, again leaving an arena match on, closed my laptop, went to my desktop and sold a card (rol, had a spare) when i went back to my laptop and back to the deck screen, my rol was back, and the cash i got from selling it was gone (so no exploit)