Firstly, welcome to the forum!
This is a known bug and it's already mentioned in the sticky thread. I suggest you to edit the title with [confirm] tag and lock it.
9. Rapid Draw problems
Symptoms: Not drawing a card you should have, despite having room for it in hand. Being forced to discard an invisible 99 cost card.
Causes: If you use card draw abilities like mind gate, electrum hourglass, and precognition, too close together, an error occurs. If you are looking at extended card art by mousing over a card while a card is drawn, that card will magically disappear. As the game keeps track of your cards in hand separately, the game will think you have an extra invisible card in hand, and force you to discard it if necessary.
