I am also having this problem. I’ve narrowed it down to the reference file relationship but can’t work out why it’s happening on some not others.
After doing some reading on the net, I saw it suggested to output clips as ref. QTs then reimport to prevent the huge analysis times of smoothcam, so I have these things all through out my project.
It’s driving me nuts as the render time on these sequences is on the big side – min 40 minutes – so re-rendering all the time is really slowing me down.
I was also finding that FCP was just randomly losing render files all the time anyway and I found that outputting ref QTs then nesting them into new sequences, along with other footage) seemed to solve that problem. For a while.
Well, the re-render of my sub-comp sequence is done, am going to nest it directly into it’s intended sequence rather than doing ref QTs and see how that goes.
“It made sense at the time”