Deaths in Match Not Credited Toward Daily "Kill 25 of your opponent's creatures" quest.
I was playing a Historic Brawl match, Liesa v. Scarab God. At least twice Liesa blocked scarab and drake tokens. I cast Massacre Wurm when the opponent had Talrand, at least 3 drake tokens, and four scarab tokens (as well as Scarab God, who, of course, does not die to Massacre Wurm) on the field. I cast Ritual of Soot, killing at least two more scarab tokens. These creatures all died, but my quest counter remains at zero.
Notably, my other daily quest, casting 20 black or green spells, DID tick up during this battle, so it is not a matter of all quests not working, but specifically the "kill creatures" quest.
Unfortunately, I do not have a log as I logged out before really thinking that I should report the bug, and of course I didn't bother to take pictures as I can't track whether the quest counter is changing during the match.
Edit: This problem repeated in my next match. Again played Ritual of Soot and killed many plant tokens as well as a few non-token creatures. Double blocked and killed Phylath. No upticks on quest counter. I took a log of this one.
If the game ends as the result of the combat, the opponent's creatures that died during that combat are not counted as killed and thus making the quest progress. I hope it's a bug and is not a game cheat behaviour done on purpose as many others like showing (most of the time after 5+ daily wins) the incorrect reward for the next win.