It looks like the cards are drawn but are invisible and unplayable. I think restarting the client when the bug happens will fix it.
My friend has the same bug. Don´t know which card caused the bug. It happened while he played a solo adventure. But it helped starting client new. The cards were visible again then.
My friend has the same bug. Don´t know which card caused the bug. It happened while he played a solo adventure. But it helped starting client new. The cards were visible again then.