Hi Steve,
Its working again!
Core melt is a company that makes fcpx plugins. they have bundles but also some free stuff. I was looking for a solution for this problem and a possible cause was these core melt plugins conflicting with fcpx.
turns out i had some of their free stuff installed, didn’t even remember. I installed them a while back on Mavericks and since I switched to Yosemite a month ago, I didn’t touch fcpx, so think that the combo with Yosemite is the problem. maybe something similar happened with you as well.
I uninstalled them and removed all the files but the problem was still there this morning, but i tried using the already made multicam clip.
just now, I gave it another try and I did 2 things so im not really sure what fixed it.
1 – I deleted the multicam clip and made a new one (so after the uninstall of these core melt plugs)
2 – I chose the custom option in the multicam window and set the fps the same as my project. My project was on 23,9fps and some videos were on 30fps. (the standard setting was 30fps) so i put it at 23,9 as well.
One of these 2 things did the trick because its working again.
hope this helps you…
Kr,
Heimen