To me it seems to be deck related. Some decks open. Some don't open.
I am unable to open my newly created BOROS deck.

Personally i think certain cards cause the issue.

The endless loading screen happens on both PC and Android app.

Same issue here on PC. I can edit SOME decks. It appears to be an issue with Alchemy-related decks for me. I can't create new Alchemy decks or edit existing ones.

same problem (on windows, through steam), even if I remake a deck I still can't edit it, tried network troubleshooting, even flushing DNS, and doing a winsock reset. then went to changing DNS servers, uninstalling with Revo Uninstaller and re-installing didnt work either. Checked for updates to network drivers too, runing as admin, anything I could think of... no dice. even tried it on my phone (ios) same problem. The fact it's happening on two seperate devices in such different ecosystems has me thinking it's a server bug.

^^Bump, I tried repairing the game files and rebuilding the deck via troubleshooting KBAs as well.

Love your game BTW, please fix <3

Log included**

The same thing is happening to me, but not only with mallets that contain the color red, but with any type of mallet

I cannot edit any of my existing decks: only create new ones, which I then cannot edit. This is much more critical than I thought it would be, as I basically cannot adjust any deck based on in-game learnings. I am running MTGA on Mac.

Same issue. Cannot edit any decks. Just loads

Deck builder is the second most important aspect of the app, please fix it. Cards are missing, the 4 card counter is bugged, using the filters is bugged, some decks do not even open if you select edit deck, it's a mess.

I can't edit imported decks, whether I've copied/pasted them internally or externally

I am able to create new decks, but after i try to select the format and after the first search (which gives results) every search finds no cards and when i save the deck the deck wont load if i try to open it.

Not able to build new or edit decks?

Same problem on IOS and the desktop client. Cannot edit certain decks. Mono green cub deck cannot be edited. Some blue decks with Aquatic Subtlety cannot be edited. Tried deleting the deck, re-importing it, without success. Manually recreated the deck but cannot edit afterwards either.

Same Issue.

commenting for elevation, same issue

ya having the same problem I made a few atempts to edit basically every colour combination available in Magic None of them seem to be loading for me and even when trying to make a new deck add fails to add any cards when you click on them

same, some decks can't edit

I have the issue on my desktop computer, with my Historic UB control list. I have tried creating the deck in several different ways but I cannot edit it. It's very frustrating as I am top 100 mythic right now and I can't work on my deck to optimize it...

Same issue, easy to reproduce. If I add Tempest Angler, deck will NOT open.

Same, also reported issue below. Red definitely seems involved. iOS/iphone

https://feedback.wizards.com/forums/918667-mtg-arena-bugs-product-suggestions/suggestions/51414796-deck-builder-not-loading

From my limited testing, seems Red cards are involved.