Gree, the Mire Sub is the reward for 300 daily wins. It comes with a +2% Building output boost. It worked the first day, but when I just got it for day 2, the bonus didn't get added in. My profile still shows +2% for the Sub, when it should show +4%.
My inventory does show 2 of the subs, and I've exited the game a few times. Nothing changed. This is a very nice boost, please get it working ASAP.