When entering 'The End' boss health bars show for a few seconds upon loading. This is not my first time to 'The End' as the Ender dragon has already been defeated.
Steps to reproduce
- Go to 'The End' (Dragon must be alive)
- Kill everything with /kill @e or just defeat the dragon normally.
- Return to the overworld.
- Go back to 'The End' again and you'll always see boss health bars for a few seconds upon loading the end even though no dragon boss or wither bosses exist.