Custom features (like custom ores) only load in when the world is first generated. If you log out and go to chunks that were not previously loaded, those features will not generate.
Linked issues
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This is a duplicate of MCPE-100700
Custom features (like custom ores) only load in when the world is first generated. If you log out and go to chunks that were not previously loaded, those features will not generate.
This is a duplicate of MCPE-100700
This is a duplicate of MCPE-100700