I tried to find differences between ConcretePanel_01_A from Prefabs, PrefabsLibrary, and PrefabsEditable. When I wanted to remove them, I noticed that while I have all three of them selected, if I hover over any other object, then actively selected prefab (the one with the white border) starts to have artifacts in its outline.

Here's a video of this issue: https://www.youtube.com/watch?v=37sI9WwtX_4 (It's longer than necessary, but I wanted to add as much context as possible to make it easier to reproduce the issue).