3 foxes (two white and one red), are named and tamed in an enclosure sealed with glass where they can't jump out of. Randomly one will just disappear with no reason, they didn't die from any damage and they shouldn't despawn as they are named. Only possible explanation is its a bug
Related issues
Comments

Thank you for your report!
We're tracking this issue in MCPE-21416, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki