Official comment
There are a large number of factors in the performance of rekordbox -- even two computers with identical hardware could act completely differently thanks to software applications, Windows services running in the background, a virus, malware, realtime antivirus scanning, file indexing, network sharing services, drivers ... the list is long.
I'll ask you to please file an inquiry ticket here and our rekordbox support team will be able to gather some additional information to assist you in resolving this issue.