I just lost my perfect record in CotC: Ardenvale to this bug. My opponent had out Razia, Boros Archangel and had given it first strike (not sure how, I didn’t check the log). I had out two creatures with vigilance as well that were big enough to survive Razia. The first one attacked and died to the first strike (how?). The second one attacked and made Razia lose damage prevention. Then the game soft locked. I could see the gem animation, but I couldn’t do anything other than quit the match. There were no vanguards on the board at the time (which is something that might have made AI decision making take a long time). I waited for several minutes and nothing happened and I still couldn’t do anything so I had to quit.
Maybe this has something to do with the vigilance change?