When leaving a world and opening a new one, certain things about the client when leaving the previous world are retained briefly in the previous world. This is most noticeable if a title was on screen when leaving a world, which will cause the title to continue to show for its remaining duration when joining another world. Other things such as the camera offset and the held item(s) from the previous world will also show briefly and will be visible if you pause immediately on world load.

To recreate enter a world and run the command /title @s times 0 200 0 to increase the length of the title to ten seconds and then run /title @s “Hello World” and quit the world. When joining a different world the title will remain on screen for the rest of the ten seconds.