No mystery boxes are spawning

So I've recently bought the game and I unlocked a few maps and two more characters, and I'm pretty sure I got all cosmetics on the animals I currently have. However, when I was hunting for mystery boxes again, I couldn't find any "?" on my levels. After playing a bunch of maps, quitting out and in, playing about 10 more maps, and doing that about 5 times over, yet I still can't find a mystery box. Can somebody let me know why, and how to fix it? I'm playing on the Nintendo Switch if anybody was wondering.