I can see my saved worlds when I start the app, but the game crashes during the loading screen at the "saving chunks" part.
This has happened to two worlds now after many hours of playing. Restarting my phone doesn't help; the worlds are inaccessible. Creating a new world works, but this has happened twice, so I have no doubt it would eventually happen to a third world.
If you can get hold of one of these crashing worlds (documents folder of the app, then games/com.mojang/minecraftWorlds/your_level_name), zip that folder and send it to [email protected].