CPU meter spikes and custio cuts out

Chances are it's a background task such as an antivirus or system indexer causing additional usage; rekordbox itself is fairly low-hardware-intensive. Check the task manager to see what else is running at the time and close / terminate it if possible.

You may also want to look at throttling your CPU to max out below 100%, and to effectively disable the Boost feature (if your processor has it) to prevent other hiccups from occurring.