I am (was) on Google with a Windows computer (I'm writing this on a mac), and when I would try to drag a card sometimes the screen would flash red (like a damage effect?) and occasionally stay red. I can't send screenshots because for some reason it works perfectly on a mac, but it basically was a semitransparent red overlay somewhat like the functioning damage effect, except that sometimes it wouldn't fade away and thus cause a softlock. Maybe it's related to the glitchy drag behavior some other comments were mentioning? It works perfectly for me now on a mac so maybe I'll try it again on windows tomorrow.
(Sorry if this is a bit long-winded! I really liked the game, it's quite fun now that I am able to play!)