I've already toggle the bonus chest before generating world, but there's no bonus chess spawning after the world is created. I noticed this bug since beta 1.17.10.22. This bug comes with seeding bug where random seed is generated instead of user input seed.
I've done the test multiple times using multiple world generation. I can confirm the bug.
Thank you for your report!
We're tracking this issue in MCPE-125872, so this ticket is being resolved and linked as a duplicate.
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