Earlier this month MTG Arena devs delayed a major update in order to make sure its polished up and ready to go. Unfortunately, that seems to have ended up in failure because while the freshly launched update has indeed fixed a bunch of bugs, it has also managed to somehow introduce twice as many new ones.
On the positive side of things, the number indicating how many cards you have in your deck is now properly highlighted and will no longer be a ghostly white on a white background. Disconnecting while creating a deck will now save your progress, while favorite decks will still remain in your favorites list even after you've edited them. The update has also fixed a bunch of issues with double-faced land cards, smoothed out the gameplay when it comes to resolving large amounts of triggered abilities, as well as prevented players from lagging out the game by repeatedly hovering over a card.
Sadly, that is where the good news ends. As a part of the current Friday Night Magic event, MTG Arena has reintroduced the highly random Momir game mode that gives players a chance to earn two rare cards. While that is perfectly fine on its own, the Momir event is so unbelievably broken that doing anything out of order, or even attempting to cancel an action, will immediately crash the match and result in a draw for both players. This sort of thing is mildly annoying when it happens by accident, but now that the bug is well known, there is an astonishingly large amount of players abusing it to no end to cancel game after game after game.
Even if you decide to take refuge in the standard play mode, there's still a couple of game-breaking bugs you'll need to contend with. Dual-faced cards have a nasty tendency to appear completely blank, certain land cards are drawn utterly invisible and you have to guess what you're putting on the board, and best of all, the deck shuffler can just randomly give you a six card hand.
So if you're willing to accept a bit of advice, I'd highly recommend staying away from MTG Arena for a day or two. This will still give you plenty of time to finish up all of your daily quests, but with the added benefit of avoiding hours of complete frustration. And if you're going to brave the wilds despite my warning, I hope you have better luck with the Momir event than I have!