When was the last time you gained dice?

I'm not 100% sure on when dice count reset. But if it's 5am, if you are sweeping between midnight and 5, then you won't get any as you already got them. If it reset at midnight, then you might have already sweeped just a bit pass midnight in the "previous day".

Dice drop rate is meh thou, so it's possible that you sweep 400 and wont get any just by pure RNG. But the more likely case is due to reset timing. I really don't like how different events have different reset time.