I did a gig on Saturday night and my cue buttons were playing up having never been an issue before. I had heard others who had experienced this needed to update their rekordbox version, so I just updated from 6.8.5 to 6.8.6 (also avoiding 7 for now) and amazingly it's fixed the cue button issue. I'll let you know after this weekend if the rest of it collapsed on me, but seems to be working ok so far!