Vanishing Sideboard when pressing "New Game" at Deck Test

{"ops":[{"insert":"Hi Guys,\n\nI built a Modern MonoG Tron with Karn, the Great Creator.\nAs i'm testing \"simulating\" a match, I drew my cards and wanted to mulligan. In this moment, my sideboard was available.\nI pressed \"New Game\", as current Mulligan draws 7, and when I do, the sideboard disappears and I'm unable to consult/search/anything.\n\nThank you.\n"}]}