Random albums duplicated into Library

Hi, for some reason around 300 songs have been duplicated without warning. I can see no connection between why those have been duplicated, CDs as well as purchased from iTunes are there. Some have the iCloud over it. I tried deleting some of these files yet I have to hide the songs after deletion from iCloud. Some of the music which I said to hide are still in the library and haven't gone away. Is there a shortcut I can do to delete this music, and have you any idea of what I did which made this happen, and how I could prevent this in future? Much appreciated for the help.

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