When you use /kill command,the custom entities will appear either ''Unknown'' or ''Cat'' in the chat,and when you pick the custom entity with the middle mouse button,you will get a Cat Spawn Egg
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Comments 3
I think the custom entities aren't in the entity class, so maybe that makes them an Unknown or entity.unknown.name. It also happens when opening the custom entity's inventory which display Unknown or entity.unknown.name.
Thank you for your report!
We're actually already tracking this issue at MCPE-38136, so we will resolve and link this ticket as a duplicate.
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This also applies to other commands which display entity name, for example /testfor