Items added to the scene don't always show in the hierarchy

Unity Engine
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1

Sometimes when I add items to the scene, they don’t show up in the hierarchy. I then can not delete them from the scene or select them within the scene to be deleted.

2

I think that this didn’t happens when you drag it to the scene over a mesh instead the hierarchy.

But when I drag to scene appear a error “Screen position out of view frustm”. But it works.

3

Happened to me once too, this helped: Can't remove GameObject from scene in editor (Not appear in heirarchy, not selectable, Ghost object) - Questions & Answers - Unity Discussions