This is an old Thread, but I encountered the same problem today. If I customize a Property in a SubCategory, the Property will be added in a new Category called Category|Subcategory.
I tried different implementations, all with the same result. Directly by calling DetailLayoutBuilder.EditCategory("Category|Subcategory") and then DetailCategoryBuilder.AddProperty(TSharedRef<IPropertyHandle> PropertyHandle) or DetailLayoutBuilder.AddPropertyToCategory(TSharedRef<IPropertyHandle> PropertyHandle)
Is there a way how you should handle this? If not and this is a bug I will create a Bug report later on.
