The action bar appears after entering or leaving any dimension and after a world has been reloaded and in different worlds.

Steps to reproduce:

1. Go to a flat world or a normal world and enter a boat (put water under it if you want to)
2. Leave the boat
3. Get some blocks away from the boat
4. Exit the world and re-enter it
5. Look at the place where the action bar appears

or

1. Run in any world:

   /title @a actionbar Hello World

2. Exit and reenter the world

Observed result:
The action bar text lingers between worlds. Restarting the game fixes the issue.

Expected result:
No action bar appears.