I have no idea what really caused the bug so here is the situation:

I was playing Simic Eldrazi in the Historic Metagame Challenge (bo3) against Boros Auras. I had an Ugin, Eye of the Storms on the battlefield and passed the turn to my opponent. They cast (or tutored with Light-Paws, can't remember) Sheltered by Ghosts and exile Ugin. Nothing strange so far. A turn or two later I attempt to look at the pile of auras under Light-Paws, considering bouncing their Sheltered with my Ugin's Binding. Except when I click on the pile, all cards are invisible and I am seemingly unable to interact with them. I eventually succeed in bouncing Sheltered by Ghosts (which stays invisible) but my Ugin seemingly doesn't return to the battlefield. I check my exile zone, and notice that the card is invisible, but clearly still appears to be there, as the other visible cards do not appear centered on screen.
I cannot win without Ugin so I concede and proceed to sideboard. Unfortunately I did not take any screenshots for this first game, but I do have some for the next game.

In the second game, things get even weirder. I immediately notice that my seven-card opening hand has 2 clear gaps in it. I'll call this phenomenon "shadow cards". So I have two shadow cards, and so does my opponent for some reason, but I keep the hand anyway and start playing to avoid timing out. I quicky notice that the shadow cards are not actually gone, as I can see what seems to be a Mind stone glowing in the middle of my deck as if I can cast it, which I attempt to do without success. Moreover, not only cards, but also triggers seem to randomly become invisible, as shown in the case of Esper Sentinel's trigger, where we can see that the trigger animation seems to stay stuck above the card without being able to reach the stack. At that point I restart Arena during my opponent's turn to see if it resolves the issues, but I can't get back into the game and get stuck on the bugged "description description description" waiting screen for over a minute, before getting the "Defeat" notification, presumably for timing out.

This is the first time that such a bug happened to me, so I think it's worth mentioning that I was simultaneously on a WhatsApp video call on my Windows PC, regularly switching between the embedded image view and the regular app window, which I don't usually do.