This bug, along with many others I have discovered, appeared after version 1.16.100 was implemented to (from what I can tell) Xbox One users.
In a world I have, in survival mode, I attempted to summon The Wither. When I did, the boss would move very slowly in a circle and it's bar until you're able to fight it would also increase quite slowly. Once you're able to finally fight it, only The Wither will lag and lose hardly any health.
Related issues
duplicates
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Thank you for your report!
We're tracking this issue in MCPE-105892, 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.
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Thank you for your report!
We're tracking this issue in MCPE-105892, 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