This time I was unlucky with chests (OK I also didn’t use that many flasks) maybe around 15 total.
But I also had months with 50+ when I was hunting scores and used a lot of flasks.
I don’t know if there is anything behind, but I normally get more chests in harder levels.
For example if I farmed easy 3 (old events) for XP and used a few flasks I often did there a few hundred runs and get maybe a handful chests.
On the same time I get for Legendary high levels nearly the same amount of chests with a single flask and under 10 runs…