Please check the attach repro project. There is a particular asset group setup with nested folders that causes "Build Player Content" to fail due to the following exception: In the repro project, there is folder named "Test" containing a subfolder "Test2". "Test2" contains an asset called "MaterialB". Now I add folder "Test" to an asset group (also called "Test"). Everything works fine, "Test2" automatically gets added to the asset group as nested folder. However, when I add "Test2" separately to the same asset group, the bundle build fails because it tries to add "MaterialB" to the asset bundle twice although it is only shown once in the Addressable window (nested below Assets/Test/Test2). I use this setup for adding labels to all assets contained in the parent folder without labeling the child folders.