Official comment
Sorry about that - we are aware of some users having an issue with the Beatport / Beatsource SDK. In these cases, we're collecting the log data and asking you to please try downgrading to rekordbox 6.6.1 to see if that works for you.
There is no loss of data between version of rekordbox, and you could have multiple versions installed simultaneously - simply run the installer, then launch the corresponding version from the application folder (not the shortcut on the start menu or desktop).
If you still have problems, please file an inquiry ticket here and our support team will gather some additional information to assist you in resolving this issue.