The triggering event components for custom blocks which is "minecraft:on_player_destroyed" didn't execute the event if you are in creative mode, when in survival mode and adventure mode this component can execute the event properly.
I believe this is a bug because every components is supposed to work whatever gamemode you are in!
Thank you for your report!
We're actually already tracking this issue at MCPE-102625, so I will resolve and link this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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