FCP: how did my mutlcam cuts-and-switches get out of sync with the clip?

Disclaimer: I'm an FCP newbie.

I created a multicam clip for a music video, and used the angle viewer and timeline to cut-and-switch between angles, and the results were very nice. That was earlier today.

When I played it later today, the movie was full of blank cuts, mostly in this pre-roll (early) portion before the song even starts playing (and was slated to eventually be trimmed off). It was just the cameras rolling early doing sound check. But I never did any cut-and-switch in that portion of the video. Where did those cuts come from?

So I scrolled to the useful part of the video where the music starts. All the video angles are still in sync with each other and the music track. But all the cuts are now happening at the wrong place and to the wrong angle. And as you can see on the screenshot, the movie now ends before the song audio is over (red arrows show audio start/stop). It's as though the cut-and-switch layer shifted on the timeline relative to the underlying clips.

Can anyone help me understand how this happened?

Another way to ask this is, how can it be fixed? Is there a way to shift the entire "cut-and-switch" overlay relative to the underlying multicam clip?

Thanks in advance!

Dave