We have a fix for at least some of the Direct Challenge issues! If you've been encountering this issue, please try again and let us know how it goes.
We were finally able to get a repro for the bug in our development environment, and we fixed the bug we found. We are not confident that this was the one and only issue here, which is why we're asking for more information, but there should be at least a significant improvement.
Fixed a bug that caused some players to consistently encounter “Error updating data” when trying to login (Specifically, this is fixed for players who had a Brawl deck saved with a Commander that had Specialize)
Updated the Packs tab in the store so that Khans of Tarkir packs note where they are and aren't legal