Please tell me about "unnamed_device" entities

They seem to be the result of some sort of glitch with a device entity. Or not?
They’re not stored in core.entity_registry – are they stored anywhere?
If not, how does Home Assistant know about them?

I have an “unnamed_device” that’s a doppleganger of an item in core.entity_registry – though that item entity is non-functional, and I can’t tell in the core.entity_registry why it’s broken.
Is there some typical/generic way to resolve unnamed_device entities?

A search run on the community forum shows many folks suffer from these. It would be helpful there be a way to repair them. If it’s already documented, please point me to it.

Thanks.