Sorry, you'll need to provide a bit more information -- from what I gather, you were using the XDJ-RX as a controller & audio interface the first time the problem occurred? I'll need some details there:
- operating system version
- DJ software & version
- XDJ-RX firmware & driver version
And then I understand you say the problem occurred again when using a USB device. More info again:
- was the USB drive prepared with rekordbox?
- was it possibly the same song that caused the issue when playing from the computer?