Lighting Bug in Unity Editor (2018.2.7f1) when instantiating prefab from AssetBundle

I'm trying to resolve a bug that occurs only in editor in my project when instantiating a prefab from an AssetBundle. In an Android build, it works just fine. See attached image for comparison.

My scene is very simple with only a baked HDRI skybox and no lights. The materials use the built-in Standard shader and are all included in the AssetBundle that I load the asset from. Drag & dropping the prefabs directly in the scene in edit mode gives perfectly normal visuals.

Again, this only happens when loading and instantiating the prefab at runtime in the editor, which makes it non-critical but still a real pain. I'm at a complete loss.

Thanks for your responses in advance!