I am a noob to FCPX, but not to the business. In fact, I started when editing meant flatbeds and splicing blocks, progressed through low and high-end linear video editing, and started with NLEs in 1990 with Montage (anybody remember those 17 betamax decks?).
I am helping a friend finish a project, inheriting their timeline and MacBook Pro (Retina 13-inch, Early 2015) that it was assembled with (using FCPX 10.3.4). The timeline is over 2.5 hours long, and has nine audio tracks synched, as well as a couple of music tracks (OK, I know you call them lanes in FCPX...). I am tackling audio first, and there are performance issues redrawing all those waveforms, so I chopped the timeline up into five roughly 30 minute chunks.
My problem is that as I am reassembling the timeline (Command A to grab everything, Command C to copy everything, and then Command V to paste each segment back to back), lots of 1 frame gaps are being introduced into the copied and pasted video lane, and some audio is slipping out of synch. I must be doing something wrong. Anyone seen this and solved it? Any insight would be appreciated.