I've got a DJM850 + two XDJ1000 myself. The only issue I had with tracks not starting in the proper point was when I loaded a new track, it would pick up the time of the previous track. I turned on the box in serato to start at the beginning of the track, and now it works as intended. I am surprised you are getting glitch sounds and music stops when using the DJM850, it works great for me.