Okay. I am not sure how this happened. I have never seen this before with previous versions. I selected all files in my library, but the option to expand was disabled.
This is how selecting all files looks for this particular artist in my library:
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I see now -- I clicked collapse stacks and now all files except for top of stacks vanished. I must have accidentally expanded them not even knowing what this did. This must be something new for MC27.