The only time a box will ever drop in Yeti Plateau is from the trees. As far as I'm aware, nothing else ever drops it, just trees. They're also infinite respawn, even after the respawn timer is up...or at least they kept spawning for like the two hours I spent there.
"If someone asks you whether or not you're ticklish, it doesn't matter what you say, they're gonna touch you. If you don't wanna be touched, you gotta say something like, 'I have diarrhea. And yes, I'm very ticklish.'"