Playing in a Samsung Note 8, unrooted, worlds being saved in main memory. Game app version says "1.20.0". Have a 30MB world in survival, and two "backup" copies of it. Yesterday I resolved to change my skin, was playing with default Steve skin. I'm playing with no account logged in. I clicked the "choose new skin" option, then browsed to one random image file. Got the "This isn't a skin file, silly" message. Then I selected a skin, the second one from "Sweater Weather" pack, which was free to use at this moment. Returned to the world, played a bit and closed the app.

Today I opened the game again, to discover that my skin returned to Steve's default, and my worlds where missing. Looked in the folder with a file explorer, and it looked empty (0 files). After some hours, had an idea: to try to change my skin back to the one I selected yesterday, to find it wasn't free anymore. I selected it anyway (didn't bought the pack, just selected it) and them hit Back. Clicked "Play" and voilá, my worlds were back.

I'll don't know how to reproduce this error, since it needs a free skin to turn into a non-free one.