Fireworks are not loaded from the saved NBT

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Requesting review:
This is straight up data loss upon reloading the world. It is not requesting a change or addition, but rather for the game not to forget a state. These issues are accepted in every other scenario as bug, so this should be no different.

While the steps to reproduce make it "intentional" to trigger this, this loss can happen whenever because of a crash of battery dying. The result is the same, the fireworks vanish.
It's also present on servers away from spawn chunks, disconnecting and reconnecting makes the fireworks vanish too, and that's not fully closing the world. Heck just teleporting away and back is enough to trigger this.

I was able to test this issue by using a repeating command block to track fireworks' lifetimes (in ticks) on a scoreboard, and by using UME to check NBT data.

The report is not accurate when it says that fireworks are not loaded when reloading the world after save & quit. What actually happens is that the firework loads and explodes before the client fully loads and gives control to the player. The fact that the world loads and gets ticked well before the player is given gains sight, sound, and control is tracked at MCPE-42310.

Fireworks have a lifetime of only 22-31 ticks. In my tests, the fastest I could save & quit after launching a firework would use up 17 ticks of the firework's life. Then, as many as 8 of these ticks would be used up during world loading.

You can also verify what is happening without using scoreboards and third-party apps. If you summon fireworks under a low ceiling in survival and then save & quit before they explode, you will take damage from the explosion during loading, before you can see or hear anything.

Dhranios' comment below describes a separate, but seemingly similar issue, where fireworks do not reappear after teleporting away and then back. I determined that the cause there is different, and I made a new report for it at MCPE-178258.

Ah, than the report was just faulty.
In that case discard the review request.