I am completely new to everything video & editing and I ran into the same issue as well. After trying everything that was suggested before, with all the updates, install/uninstall etc., I simply went to user preferences in FCP, under the “render control” tab, down below under the “master templates & motion projects” section, I simply changed the quality from “normal” to “best”. Seems simple, and I am the last person to make suggestions, but this is what worked for me when all the other attempts did not. I hope this helps someone.