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@Gary > Sorry to hear about this. I'll direct you to file an inquiry ticket here so our rekordbox support team can gather additional information to troubleshoot and resolve this issue for you.
So you're aware, the reason the export mode (linking to players) is so much less intensive on your system resources is the players themselves are doing all the gruntwork of processing the audio, the computer essentially acts as a hard drive with a screen. In export mode, your computer is having to manage all the audio buffering, manipulation, and processing.