Torches provide light to only own block and darken rest of chunk

I think you might have miscalculated your chunk boundaries. The torch may be in a separate chunk from the rest of the room. For positive coordinates the first block is 0, x, 0, so the corners will be odd numbers (multiples of 16, minus 1).

That being said, this is a bug that light is not updating properly across chunk boundaries. See MCPE-56795 or MCPE-58182.

Thank you for your report!
However, this issue is a Duplicate of MCPE-58182.

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