I had 5 axolotls in an enclosure. They were there through multiple games sessions. When I went to add 2 more axolotls I noticed 1 was missing. I went to bucket tropical fish for breeding. When I returned only the 2 recent additions were remaing. The 4 remaining originals were gone.
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