Please reset your RX using the following steps:
1. Disconnect the USB from the RX
2. Turn on the power of RX while pressing [SHIFT] button on the left deck and [DECK 1] button at the same time.
3. Wait for about 5 seconds.
4. Press the [SYNC] button on the both decks for 3 seconds.
When the [SYNC] buttons' LED is off, reconnect the USB and launch rekordbox to see if the latency has improved.