I have encountered a bug on my MCPE world where mobs have stopped dropping anything. They don't drop items or XP.

Blocks still drop, and mobs still shoot projectiles, but mobs don't drop anything when they die. It started when I got the Passing the Time achievement. I wasn't sure what I did to get it, so I clicked on the pop up. It took me to the achievements menu, and I found that I had spent 100 days in my world. I looked at the hairstyle I got from it, then went back to my game. After that, I couldn't get any materials or anything from mobs.