Why do mobs keep despawning even when named?

Solution 1:

There are a few possibilities as to what is happening:

1. You are using a very old device that cannot handle newer versions of Minecraft. As more new features are added to Minecraft, it becomes gradually more difficult for devices to handle, as it requires more power (CPU, RAM, etc). Sometimes in situations like these Minecraft can glitch in this way.
2. Your Minecraft app is corrupted. On very rare occasions, Minecraft can install the improper way, causing ridiculous bugs and other issues. You can normally fix this by reinstalling the app.
3. Minecraft has a bug. This is most likely the issue, as this issue has been reported multiple times to Mojang.