I know I’m a month behind on this post so I am sure that you either already figured out what you needed to or made do. However I think I figured out the issue. I noticed that some of my multiclips played back only one clip in the viewer once my render bar for that section was blue. Switching the angle, which I imagine causes the clip to become unrendered, changes the render bar back to green over the selected clip allowing all angles to be viewed while in open sync.
I also just tried trashing my render folder and got the same results. Don’t know why this ocurrs but hopefully this helps down the road for people.