I have tried several times to migrate my catalog from the old desktop Lightroom to the new CC Lightroom. I have optimized my catalogue, removed any missing photos, and tried to find any photos with conflicting metadata. Every time I run the migration it comes back with 1 asset with a metadata conflict and fails immediately. I have found no photos in the desktop version that have conflicting metadata by running a smart filter on my entire catalogue.
I've contacted Adobe support several times, at maybe an hour each time with no luck in fixing the issue. The last time I was working with a tech we got disconnected and i was never able to get back in touch with him immediately after the call.