In the first day of Viking festival, I obtained 3 chests for 31 crowns and the first 2 for the first 17 crowns (from 14 crowns). In my opinion, it’s a bug.
I’m not sure if this topic is written in correct section.
1st chest: 297 rewards + XP luck weapon.
2nd chest: 421 rewards.
3rd chest: 568 rewards.
I think I’ve been more unlucky than usual for rewards.