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Having an i7 processor doesn't automatically mean your computer is going to run things properly -- if there are other background tasks occupying the system, that's going to cause problems. For example, was rekordbox still analysing tracks while you were playing? Was there an antivirus scan running?
I would suggest you file a rekordbox inquiry here and our support teams will be able to assist you further. As it is Christmas break, you will find a bit of a delay in response, but we will get you the help you need.