Steps to reproduce:
When you will apply add-on with new structure template features which include entities in them game will be always be crashing while loading new chunks.
Expected results: The game will load new chunks with new custom features and entities in it.
Observed results: game will crash after loading new chunk with "minecraft:structure_template_feature" which include entities in it.
Thank you for your report!
We're actually already tracking this issue at MCPE-63387, so I will resolve and link this ticket as a duplicate.
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