After playing a ranked game using a FS deck, I come back to the main menu to see an unnamed UD deck on the deck sidebar. When I clicked on deck manager, I got this screen and the game became unresponsive - I had to force it closed. I have never named a deck Doomballs the Third.
This seems to happen totally randomly. I haven't found any pattern. Once it happened right after starting the game, before doing anything else. It is rare though and its fine after restarting the game.
The pattern is: Anytime when you enter lobby (either start the whole game or return from any match) initializing your decks can fail. Note: "Current Deck: Name of Deck" and UD symbol in this screenshot: "Doomballs the Third" was probably the first instance for some kind of testing purposes in the database: