The solution at the moment seems to be to replace all your multiclips (even collapsed) with the original clips that haven’t been in a multiclip. One way to do this is; 1. Collapse your timeline, 2. Then, match frame each edit to its source clip and replace the clip. Do this for all clips in your timeline.
You then should be able to export into color etc…
My advice is, if you are going to start any new multicam projects, use 5.1.4. It worked really well, compared to 6 which just doesn’t!!!