Sideboard Showing Too Many Cards
Began adding cards to my sideboard while deckbuilding, and I noticed that while I thought it had only added 3 copies of Duress to the Sideboard, 4 were showing up. I removed one, and it dropped to showing 2 copies of Duress, so I added one back in and it displayed 3 copies again. However, now there were 4 copies of Glistening Deluge instead of the 3 that were supposed to be there, and I also noticed that there were eight cards in the Top 7 slots of the sideboard.
Out of curiosity, I then started switching cards around between the Bo3 Only part of the sideboard and the Top 7, and cards in the Top 7 seemingly began duplicating themselves whenever I moved a card between Top 7 and Bo3 Only. Eventually I reached a point where there were maybe eight copies of Duress shown in my Top 7, and when I did another swap, the game lagged a ton and I saw what's shown in the attached screenshot. When I tried scrolling down, the game had another lag spike, but the little light grey scroll bar on the right hand side did move down the screen a little bit. I didn't try scrolling to the bottom, as the PT OTJ stream I had playing in the background had already frozen when I initially tried scrolling.
In case it's relevant, the version of Duress that I was using is the STX Mystical Archives one with a gold background, and I was playing Arena on a Mac using EpicGames.
Update: I was able to recreate the bug with other cards as well, so I think this bug just happens whenever you swap cards between the Top 7 and the Bo3 Only sections of your sideboard. Attached another screenshot of me recreating the bug with Brokers Initiate and Pixie Illusionist, as well as screenshots of me "duplicating" cards in the original sideboard that I encountered this bug in.