[2023] DAY 3 GIVE IT UP FOR DAY 3!

We just released an update that should have fixed this (no client, back-end only). Please let us know if you're still having problems

We've got a hopeful fix for DC issues in this release as well! We've had trouble repro'ing the issue, and though we've gotten some issues to repro now, we're not sure we're seeing exactly what players are. We've fixed at least one bug that could cause the problem you describe, so give it another shot and let us know how it goes.

Short version, since (given holidays) I'm not sure when/if we'll get a longer article out:
With the KTK/Timeless release we added support for the restricted list. As part of this, we added a new chunk of logic to our deck validation code to look over each card in the deck, check whether it was restricted, and, if so, check that it met the count restrictions.

While doing this check, the code makes the seemingly simple assumption that everything in your deck is a card. Now, this sounds silly - what else would you put in your deck that's not a card? But, internally, we have a lot of data that looks & acts like a card, but isn't really a card. Tokens are an obvious example, but there are also things like the spell portion of an Adventure card, or something like Ribbons (from Amonkhet's Cut // Ribbons), or the back side of a traditional double-faced card, etc. There are lots of these, but they shouldn't ever be part of a deck directly. You don't put Stomp in your deck, you put in Bonecrusher Giant.

Except, of course, that this is Magic, a game composed less out of rules, and more out of a complex network of exceptions to the rules. And there's one case where you should actually have a not-really-a-card in your deck: that's how we keep track of which additional color you've selected for a specialize commander in Brawl. (Did you know that, when using a card with Specialize as your Commander, you can choose one (and only one) other color to count as part of their color identity?)

For example, if you had Lae'zel, Githyanki Warrior as your commander (A wise choice, human. but know that she serves not you but Vlaaktih alone), and you wanted to build a red-white deck, you would pick red as the extra color and we would store Lae'zel, Wrathful Warrior in your actual deck. This isn't a really-for-real card, but it's enough like a card that this still works.

At least, it worked until it ran into that new code checking the restricted list, which expected everything to be an actual card, not a card-shaped object like those specialized forms of cards. So the code ran into something it didn't expect, errored out, and that's what prevented players from being able to log in. Thanks to some great debugging help from the community, we were able to quickly narrow down on a cause, which helped us deliver a fairly quick fix. (Though we're always sorry for any amount of time a player can't log in.)