Ever since the 10.3 update, I'm having regular problems with the share to youtube function. Basically, it now fails at least 50% of the time. What happens is that it exports the project fine and starts uploading, then at one point (usually when it's just about to finish) it just stops and FCPX displays an error message : Publishing to YouTube Failed: The operation couldn’t be completed. (com.google.HTTPStatus error -1001.) . In youtube I just get a video that says "uploading, 0% ".
Strange thing is, I never had any such problems before 10.3 and I do a lot of those "publish to youtube" from FCPX, they're an essential part of my work, and at the moment it's really annoying to have to go through the cache folder to pick my files and upload them to youtube manually.