I have been doing Explore 12 battles all day long using my Fireblade+Zuul team, so we’re talking about less than 3 minutes per run (each battle is 20-30 sec average, sometimes longer if I lose my hero due to bad luck).
And I’ve done a LOT of battles today… with zero mimics. Yet last night on Android right after the update, I was getting mimics nearly every other boss chest. I got the 3 mimic achievement last night. I even got the Hoard Mimic.
Yet on Steam today? Nothing. Not a one.