I forgot to mention that since migrating, I've been intermittently leaving Lightroom CC open overnight so it can sync my photos to the cloud. It's been almost 3 weeks and it's only 5% complete...
I think you should stop using LR CC and go back to Classic.
That said, I'm enjoying using LR CC but with a relatively small number of files. Additionally, most of the known online teachers strongly suggest that you not use them in any connected way. Use one or the other.
Done and done.
I use Lr CC for iPhone captured Photos (Lr camera of phone camera) + the desktop version.
For photos from other cameras (Canon) I use the Bridge/Camera Raw/Photoshop workflow.
I use Lr Classic (always with sync paused) for things like the Slideshow or Web Module of if there is a particular preset there I would like to use.
I've spent hours testing ways to use both Lr versions syncing simultaneously and it has always ended in a mess.
Use one or the other - but never both for the same batch of photos.