devtrackers.gg
already reported and working on a fix. The bug comes with the fact that none of the celestials count as being owned by the player, so they fail the deck validation. should be fixed soon.
This bug is quite weird. It means they check for deck integrity before putting you into the play queue, in addition to checking when you close and save a deck. But what attribute would they be checking for that throws a flag for Celestial deck art? Only thing I can think of is that a playtester put Celestials directly into their deck and this line of code checks that there are no Celestial cards in the deck.
you can have cards and by extension, deck covers you don't own in your deck, like when you import a deck you don't have all the cards for. we let you save the deck, modify the deck, but the cover card is failing the same check that won't let you queue with a deck you don't have cards for