I've experienced this issue multiple times on Minecraft PE (iOS) after installing v1.1.0. It seems to occur when I have more than one mob following me. For example, the game has crashed repeatedly when I have two tame wolves following me. When I restart, the wolves have disappeared completely. I just experienced the issue again when I had three cows and a tame wolf following me home. All four mobs are now gone. After the crashes, I've also noticed mobs disappearing from a farm I had set up.
I believe so. I've seen it a lot since the update, usually when multiple mobs are following me. I wanted to add that piece of info and add my voice so they know multiple people are having the issue. Thank you for reporting!