Hello!
Nope, sadly I never did fix it… I may have understood it though.
I removed the stills and since then it has rendered normally. At first, I simply downres-ed the stills but that just delayed the message popping up. I guess that smae as the stills, the 3 layers may be too much for fcp to handle as it can only use 2.5 GB max. They’d better hurry up and improve on that cos it’s damn unpractical!!
Good luck… Please let me know if you do fix it…