Bpm

I guess you used the dynamic BPM analysis in Rekordbox. Try using the static analysis.

Not sure how to do that but I will look into thanks does it make the bpm more stable

@Bren > Have you prepared your tracks through rekordbox? If you are letting the player read the tracks, it has to dynamically analyze the audio on the fly. With rekordbox, the track will have BPM data stored from the software analyzing the waveform. @Voke's referral to dynamic / normal analysis mode has to do with the algorithm used to read the BPM if the song has a consistent beat or a live drummer with a wavering tempo.

As for the track not loading until it has finished, that's called load-lock; try pressing play/pause or cue to stop the playback, then load the next song.

I have loaded the tracks into rekordbox them sent them via wifi to the aero and also tried doing it via the usb memory stick but they still don't seem stable I'm not the best at using rekordbox but still thought these bpms would stay constant, the load lock seems to happen more after the track has finished so if it has run right to then end then I can't seem to add another track to that side of the unit @pulse

If the track has finished, the player may still consider it as being "active," try pressing the CUE button on that deck and it will stop, allowing you to load a new track.

As for the BPMs, look into the dynamic / normal mode analysis within the rekordbox settings.