Yeah it's duplicate. Sorry for not noticing that issue.
Note: The user interface switches between the 2 screenshots given every 0.1 second (approximately), giving the user a "blinking" view.
Will fix when exiting & re-entering the game
Duplicate to MCPE-119628
and this firework rocket disappears after exiting and re-entering the world.
As an additional information, this firework rocket can not be removed even by placing a block in its position or placing water/lava above. When placing lava above it, a fire on it starts to appear, but the firework rocket remains after minutes of burning with lava.
Can confirm. The issue exists with nether biomes, end biomes, and "the void".
Structures will generate (e.g. end cities in "End Highlands") and mobs will spawn (e.g. ghasts in "Nether Wasteland"), but the terrain is completely different and filled with grass blocks (some with stone underneath) and oceans / rivers. There were also random noise caves and mountains.
I've attached 5 more screenshots in MC-258176 (which was a duplicate).