This conversation has been merged. Please reference the main conversation: Lightroom: Keywords don't sync between CC and Classic
However, the same could not be said for keywords (which, of course, are only relevant to LR CC, but not CC for Web). First off, I discovered that LR CC was only picking up keywords that had been written as metadata to disk. That means that before syncing a collection from LR Classic, I needed to save metadata to file. If I had already synced the collection and then saved the metadata, the changes were not picked up by LR CC. Even if I quit and restarted the program, the metadata was not reloaded. And that's despite the fact that LR Classic would immediately sync the file anew whenever I saved the metadata to file.
The only way I could get LR CC to re-read the metadata was to first stop syncing the collection from within LR Classic, then to delete all the individual photos from the "All Photos" view within LR CC, and then to sync the collection again.
(Incidentally, related to this is the issue of how to control which keywords are written to file. I had indicated not to export certain keywords, yet those were still saved as metadata and picked up by LR CC. And even this behavior was not consistent. Certain higher-level keywords appear to have been applied to some photos but not others within the same album.)
Another issue is that there doesn't seem to be a way to edit keywords. At some point, I had corrected the spelling for someone's name keyword on LR Classic. The earlier spelling seems to have been saved to metadata, because when I synced a photo of the person, LR CC had a keyword for each spelling. I could remove the incorrect keyword from the individual photo, but there didn't seem to be a way to do this across the whole system.